This patch fixes a number of data type aggregation problems in IN and CASE:
- MDEV-11497 Wrong result for (int_expr IN (mixture of signed and unsigned expressions))
- MDEV-11514 IN with a mixture of TIME and DATETIME returns a wrong result
- MDEV-11554 Wrong result for CASE on a mixture of signed and unsigned expressions
- MDEV-11555 CASE with a mixture of TIME and DATETIME returns a wrong result

1. The problem reported in MDEV-11514 and MDEV-11555 was in the wrong assumption
that items having the same cmp_type() can reuse the same cmp_item instance.
So Item_func_case and Item_func_in used a static array of cmp_item*,
one element per one XXX_RESULT.

TIME and DATETIME cannot reuse the same cmp_item, because arguments of
these types are compared very differently. TIME and DATETIME must have
different instances in the cmp_item array. Reusing the same cmp_item
for TIME and DATETIME leads to unexpected result and unexpected warnings.

Note, after adding more data types soon (e.g. INET6), the problem would
become more serious, as INET6 will most likely have STRING_RESULT, but
it won't be able to reuse the same cmp_item with VARCHAR/TEXT.

This patch introduces a new class Predicant_to_list_comparator,
which maintains an array of cmp_items, one element per distinct
Type_handler rather than one element per XXX_RESULT.

2. The problem reported in MDEV-11497 and MDEV-11554 happened because
Item_func_in and Item_func_case did not take into account the fact
that UNSIGNED and SIGNED values must be compared as DECIMAL rather than INT,
because they used item_cmp_type() to aggregate the arguments.
The relevant code now resides in Predicant_to_list_comparator::add_value()
and uses Type_handler_hybrid_field_type::aggregate_for_comparison(),
like Item_func_between does.

As agreed with Sanja, debug messages printed in
Item_func_in::fix_length_and_dec() now have the "DBUG:" prefix,
to make the *.result files more readable.
Also changing level from WARN_LEVEL_WARN to WARN_LEVEL_NOTE.

MDEV-11503 Introduce Type_handler::make_in_vector() and Item_func_in_fix_comparator_compatible_types()

This patch implements the task according to the description:

1. The old code from Item_func_in::fix_length_and_dec() was decomposed
into smaller methods:
- all_items_are_consts()
- compatible_types_scalar_bisection_possible()
- compatible_types_row_bisection_possible()
- fix_in_vector()
- fix_for_scalar_comparison_using_bisection()
- fix_for_scalar_comparison_using_cmp_items()
- fix_for_row_comparison_using_bisection()
- fix_for_row_comparison_using_cmp_items()

The data type dependend pieces where moved as methods to Type_handler.

2. Splits in_datetime into separate:
   - in_datetime, for DATETIME and DATE,
   - in_time, for TIME
   to make the code more symmetric across data types.

Additionally:
- Adds a test func_debug.test to see which calculation strategy
  (bisect or no bisect) is chosen to handle IN with various arguments.
- Adds a new helper method (to avoid duplicate code):
  cmp_item_rows::prepare_comparators()
- Changes the propotype for cmp_item_row::alloc_comparators(),
  to avoid duplicate code, and to use less current_thd.
- Changes "friend" sections in cmp_item_row and in_row from
  an exact Item_func_in method to the entire class Item_func_in,
  as their internals are now needed in multiple Item_func_in methods.
- Added more comments (e.g. on bisection, on the problem reported in MDEV-11511)

- Removes "Item_result Item_func_opt_neg::m_compare_type" and introduces
  "Type_handler_hybrid_field_type Item_func_opt_neg::m_comparator" instead.

- Removes Item_func_between::compare_as_dates, because
  the new member m_comparator now contains the precise information
  about the data type that is used for comparison, which is important
  for TIME vs DATETIME.

- Adds a new method:
  Type_handler_hybrid_field_type::aggregate_for_comparison(const Type_handler*),
  as a better replacement for item_cmp_type(), which additionally can handle
  TIME vs DATE/DATETIME/TIMESTAMP correctly. Additionally, it correctly
  handles TIMESTAMP which fixes the problem reported in MDEV-11482.
  The old compare_as_dates/find_date_time_item() based code didn't handle
  comparison between TIME and TIMESTAMP correctly and erroneously used TIME
  comparison instead of DATETIME comparison.

- Adds a new method:
  Type_handler_hybrid_field_type::aggregate_for_comparison(Item **, uint nitems),
  as a better replacement for agg_cmp_type(), which can handle TIME.
- Splits Item_func_between::val_int() into pieces val_int_cmp_xxx(),
  one new method per XXX_RESULT.
- Adds a new virtual method Type_handler::Item_func_between_val_int()
  whose implementations use Item_func_between::val_int_cmp_xxx().
- Makes type_handler_longlong and type_handler_newdecimal public,
  as they are now needed in item_cmpfunc.cc.

Note:
This patch does not change Item_func_in to use the new aggregation methods,
so it still uses collect_cmp_type()/item_cmp_type() based aggregation.
Item_func_in will be changed in a separate patch and item_cmp_type() will be
removed.

This is an extraction from the patch for MDEV-10577, which is not
directly related to %TYPE implementation. This patch does the following:
- Moves LEX::set_last_field_type() to Column_definition::set_attributes()
- Adds initialization of Column_definition members length, decimals,
  charset, on_update into the constructor.
- Column_definition::set_attributes() now does not set length and decimal
  to 0 any more, as they are not initialized in the constructor.
- Move Column_definition::prepare_interval_field() from field.h to field.cc,
  as it's too huge.

MDEV-11365 Split the data type and attribute related code in Item_sum_hybrid::fix_fields into Type_handler::Item_sum_hybrid_fix_length_and_dec()

This patch:
- Implements the task according to the description
- Adds a new class Type_handler_numeric as a common parent
  for Type_handler_real_result, Type_handler_int_result,
  Type_handler_decimal_result, to share the common code
  between numeric data type handlers.
- Removes the dedundant call for collation.set(item->collation) in
  Item_sum_hybrid::setup_hybrid(), because setup_hybrid() is called
  either after fix_length_and_dec() or afte ther constructor
  Item_sum_hybrid(THD *thd, Item_sum_hybrid *item),
  so the collation is already properly set in all cases.

This patch:
- Adds a new virtual method Type_handler::Item_get_cache
- Splits moves Item_cache::get_cache() into the new method, every
  "case XXX_RESULT" to the corresponding Type_handler_xxx::Item_get_cache.
- Adds Item::get_cache as a convenience wrapper, to make the caller code
  shorter.
- Changes the last argument of Arg_comparator::cache_converted_constant()
  from Item_result to "const Type_handler *".
- Removes subselect_engine::cmp_type, subselect_engine::res_type,
  subselect_engine::res_field_type and derives subselect_engine
  from Type_handler_hybrid_field_type instead.
- Makes Type_handler_varchar public, as it's now needed as the
  default data type handler for subselect_engine.

MDEV-11347 Move add_create_index_prepare(), add_key_to_list(), set_trigger_new_row(), set_local_variable(), set_system_variable(), create_item_for_sp_var() as methods to LEX

Moving another banch of functions implemented in sql_yacc.yy as methods to LEX,
to be able to reuse them between sql_yacc.yy and sql_yacc_ora.yy easier.
The list of functions:
- add_create_index_prepare()
- add_key_to_list()
- set_trigger_new_row()
- set_local_variable()
- set_system_variable()
- create_item_for_sp_var()

This patch:
- Introduces a new virtuial method Type_handler::set_comparator_func
  and moves pieces of the code from the switch in
  Arg_comparator::set_compare_func into the corresponding
  Type_handler_xxx::set_comparator_func.
- Adds Type_handler::get_handler_by_cmp_type()
- Moves Type_handler_hybrid_field_type::get_handler_by_result_type() to
  a static method Type_handler::get_handler_by_result_type(),
  for symmetry with similar methods:
  * Type_handler::get_handler_by_field_type()
  * Type_handler::get_handler_by_real_type()
  * Type_handler::get_handler_by_cmp_type()
- Introduces Type_handler_row, to unify the code for the scalar
  data types and the ROW data type (currently for comparison purposes only).
- Adds public type_handler_row, as it's now needed in item_row.h
- Makes type_handler_null public, as it's now needed in item_cmpfunc.h
  Note, other type_handler_xxx will become public as well later.
- Removes the global variable Arg_comparator::comparator_matrix,
  as it's not needed any more.

Also fixes:
MDEV-11331 Wrong result for INSERT INTO t1 (datetime_field) VALUES (hybrid_function_of_TIME_data_type)
MDEV-11333 Expect "Impossible where condition" for WHERE timestamp_field>=DATE_ADD(TIMESTAMP'9999-01-01 00:00:00',INTERVAL 1000 YEAR)

This patch does the following:
1. Splits the function Item::save_in_field() into pieces:
- Item::save_str_in_field()
- Item::save_real_in_field()
- Item::save_decimal_in_field()
- Item::save_int_in_field()

2. Adds the missing "no_conversion" parameters to
   Item::save_time_in_field() and Item::save_date_in_field(),
   so this parameter is now correctly passed to
   set_field_to_null_with_conversions().
   This fixes the problem reported in 11333.

3. Introduces a new virtual method Type_handler::Item_save_in_field()
   and uses the methods Item::save_xxx_in_field() from the implementations
   of Type_handler_xxx::Item_save_in_field().

These changes additionally fix the problem reported in MDEV-11331,
as the old code erroneously handled expressions like
COALESE(datetime-expression) through the STRING_RESULT branch of
Item::save_in_field() and therefore they looked like string type expressions
for the target fields. Now such expressions are correctly handled by
Item::save_date_in_field().

The full list of functions moved:
int case_stmt_action_expr(LEX *, Item* expr);
int case_stmt_action_when(LEX *, Item *when, bool simple);
int case_stmt_action_then(LEX *);
bool add_select_to_union_list(LEX *,bool is_union_distinct,  bool is_top_level);

This is a preparatory change for "MDEV-10142 PL/SQL parser",
to reuse the code easier between sql_yacc.yy and coming soon sql_yacc_ora.yy.

MDEV-11294 Move definitions of Derivation, DTCollation, Type_std_attributes from field.h and item.h to sql_type.h

Some upcoming tasks, e.g.:
- MDEV-10577 sql_mode=ORACLE: %TYPE in variable declarations
- MDEV-10914 ROW data type for stored routine variables

will need to reuse the code implemented in prepare_create_field(),
sp_prepare_create_field(), prepare_blob_field().

Before reusing this code, it's a good idea to move these global functions
as methods to Column_definition.

This patch:
- actually moves prepare_create_field(), sp_prepare_create_field(),
  prepare_blob_field() as methods to Column_definition
- makes sp_prepare_create_field() call prepare_create_field() at the end,
  to avoid duplicate code in MDEV-10577 and MDEV-10914.
- changes the return data type for prepare_create_field() from int to bool,
  to make it consistent with all other functions returning "ok" or "error".
- moves the implementation sp_head::fill_field_definition() from sp_head.cc
  to sp_head.h, as it now uses globally visible Column_definition methods,
  and is very simple, so inlining is now possible.
- removes the unused "LEX*" argument from sp_head::fill_field_definition()

There was a duplicate code to create TYPELIB from List<String>:
- In typelib() and mysql_prepare_create_table(), which was used to initialize
  table fields.
- create_typelib() and sp_prepare_create_field(), which was used to initialize
  SP variables.
create_typelib() was incomplete and didn't check for wrong SET values.

Fix:
- Moving the code from create_typelib() and mysql_prepare_create_field()
  to news methods Column_definition::create_interval_from_interval_list()
  and Column_definition::prepare_interval_field().
- Moving the code from calculate_interval_lengths() in sql_table.cc
  to a new method Column_definition::calculate_interval_lengths(), as it's now
  needed only in Column_definition::create_interval_from_interval_list()
- Reusing the new method Column_definition::prepare_interval_field() in both
  mysql_prepare_create_table() and sp_prepare_create_field(), instead of the
  old duplicate code pieces
- Removing global functions typelib() and create_typelib()

This patch also fixes:
MDEV-11155 Bad error message when creating a SET column with comma and non-ASCII characters
The problem was that ErrCongString() was called with a wrong "charset" parameter.

        JSON depth calculation fixed.

        String insertion fixed.

        The Item_func_json_contains_path was mistakenly set with the
        no '*' paths limitation.

MDEV-11562 Assertion `js->state == JST_VALUE' failed in check_contains(json_engine_t*, json_engine_t*).

        check_contains() fixed. When an item of an array is a complex
        structure, it can be half-read after the end of the recursive
        check_contains() call. So we just manually get to it's ending.

in slow shutdown mode don't stop purge threads until they've
purged everything there is

in slow shutdown mode stop all bg threads that might generate
new undo records to purge before stopping purge threads.

in slow shutdown mode purge threads really must exit only when there is
nothing to purge. Restore the trx_commit_disallowed check and
don't stop purge threads until all connection thread transactions
are gone.

The patch for bug mdev-10882 tried to fix it by providing an
implementation of the virtual method build_clone for the class
Item_cache. It's turned out that it is not easy provide a valid
implementation for Item_cache::build_clone(). At the same time
if the condition that can be pushed into a materialized view
contains a cached item this item can be substituted for a basic
constant of the same value. In such a way we can avoid building
proper clones for Item_cache objects when constructing pushdown
conditions.

* rpm upgrade fix
* update test results
* valgrind warning

        Now JSON functions return warnings if arguments are invalid.

name innodb background threads as such

MDEV-11518 Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' failed in Field_long::val_int()

QUICK_RANGE_SELECT::init_ror_merged_scan() should
also set and restore TABLE::vcol_set