Problem:
=======
  - During alter rebuild, document read from old table is tokenzied
parallelly by innodb_ft_sort_pll_degree threads and stores it
in respective merge files. While doing the parallel merge, InnoDB
wrongly skips the root level selection of merging buffer records.
So it leads to insertion of merge records in non-ascending order.

Solution:
==========
  Build selection tree for the root level also. So that root of
selection tree can always contain sorted buffer.

Also, adding 10.2 related changes for MDEV-22579

In commit b1742a5c we forgot
FLUSH TABLES, potentially causing errors for MyISAM system tables.

The rw_lock_stats were incorrectly updated.
While global statistics have limited usefulness, we cannot
remove them from a GA version. This contribution is slightly
improving performance in write workloads.

The code erroneously allowed both:
INSERT INTO t1 (vcol) VALUES (DEFAULT);
INSERT INTO t1 (vcol) VALUES (DEFAULT(non_virtual_column));

The former is OK, but the latter is not.
Adding a new virtual method in Item:

virtual bool vcol_assignment_allowed_value() const { return false; }

Item_null, Item_param and Item_default_value override it.

Item_default_value overrides it in the way to:
- allow DEFAULT
- disallow DEFAULT(col)

If the InnoDB buffer pool contains many pages for a table or index
that is being dropped or rebuilt, and if many of such pages are
pointed to by the adaptive hash index, dropping the adaptive hash index
may consume a lot of time.

The time-consuming operation of dropping the adaptive hash index entries
is being executed while the InnoDB data dictionary cache dict_sys is
exclusively locked.

It is not actually necessary to drop all adaptive hash index entries
at the time a table or index is being dropped or rebuilt. We can let
the LRU replacement policy of the buffer pool take care of this gradually.
For this to work, we must detach the dict_table_t and dict_index_t
objects from the main dict_sys cache, and once the last
adaptive hash index entry for the detached table is removed
(when the garbage page is evicted from the buffer pool) we can free
the dict_table_t and dict_index_t object.

Related to this, in MDEV-16283, we made ALTER TABLE...DISCARD TABLESPACE
skip both the buffer pool eviction and the drop of the adaptive hash index.
We shifted the burden to ALTER TABLE...IMPORT TABLESPACE or DROP TABLE.
We can remove the eviction from DROP TABLE. We must retain the eviction
in the ALTER TABLE...IMPORT TABLESPACE code path, so that in case the
discarded table is being re-imported with the same tablespace identifier,
the fresh data from the imported tablespace will replace any stale pages
in the buffer pool.

rpl.rpl_failed_drop_tbl_binlog: Remove the test. DROP TABLE can
no longer be interrupted inside InnoDB.

fseg_free_page(), fseg_free_step(), fseg_free_step_not_header(),
fseg_free_page_low(), fseg_free_extent(): Remove the parameter
that specifies whether the adaptive hash index should be dropped.

btr_search_lazy_free(): Lazily free an index when the last
reference to it is dropped from the adaptive hash index.

buf_pool_clear_hash_index(): Declare static, and move to the
same compilation unit with the bulk of the adaptive hash index
code.

dict_index_t::clone(), dict_index_t::clone_if_needed():
Clone an index that is being rebuilt while adaptive hash index
entries exist. The original index will be inserted into
dict_table_t::freed_indexes and dict_index_t::set_freed()
will be called.

dict_index_t::set_freed(), dict_index_t::freed(): Note that
or check whether the index has been freed. We will use the
impossible page number 1 to denote this condition.

dict_index_t::n_ahi_pages(): Replaces btr_search_info_get_ref_count().

dict_index_t::detach_columns(): Move the assignment n_fields=0
to ha_innobase_inplace_ctx::clear_added_indexes().
We must have access to the columns when freeing the
adaptive hash index. Note: dict_table_t::v_cols[] will remain
valid. If virtual columns are dropped or added, the table
definition will be reloaded in ha_innobase::commit_inplace_alter_table().

buf_page_mtr_lock(): Drop a stale adaptive hash index if needed.

We will also reduce the number of btr_get_search_latch() calls
and enclose some more code inside #ifdef BTR_CUR_HASH_ADAPT
in order to benefit cmake -DWITH_INNODB_AHI=OFF.

When neither MSAN nor Valgrind are enabled, declare
Field::mark_unused_memory_as_defined() as an empty inline function,
instead of declaring it as a virtual function.

This allows us to remove our own declarations of functions and structures
that are declared in the history.h file.

MDEV-22073 MSAN use-of-uninitialized-value in
collect_statistics_for_table()

Other things:
innodb.analyze_table was changed to mainly test statistic
collection. Was discussed with Marko.

The issue here was that when the schema was changed the value for the THD::server_status
is ored with SERVER_SESSION_STATE_CHANGED.
For custom aggregate functions, currently we check if the server_status is equal to
SERVER_STATUS_LAST_ROW_SENT then we should terminate the execution of the custom
aggregate function as there are no more rows to fetch.
So the check should be that if the server status has the bit set for
SERVER_STATUS_LAST_ROW_SENT then we should terminate the execution of the
custom aggregate function.

Other things:
- Removed innodb_encryption_tables.test from valgrind as it
  takes a REALLY long time

fix_fields_for_tvc() could call fix_fields() for Items that have
already been fixed before. Changing fix_fields() to fix_fields_if_needed().

For the case when the optimizer does the IN-EXISTS transformation,
the equality condition is injected in the WHERE OR HAVING clause of
the subquery. If the select list of the subquery has a reference to
the parent select make sure to use the reference and not the original
item.

On a checksum failure of a ROW_FORMAT=COMPRESSED page,
buf_LRU_free_one_page() would invoke buf_LRU_block_remove_hashed()
which will read the uncompressed page frame, although it would not
be initialized. With bad enough luck, fil_page_get_type(page)
could return an unrecognized value and cause the server to abort.

buf_page_io_complete(): On the corruption of a ROW_FORMAT=COMPRESSED
page, zerofill the uncompressed page frame.

This essentially reverts commit b393e2cb.

The leak might have been fixed, but because the
DEBUG_SYNC instrumentation for InnoDB purge threads was reverted
in 10.5 commit 5e62b6a5
as part of introducing a thread pool, it is easiest to revert
the entire change.

TRUNCATE(decimal_5_5) erroneously tried to create a DECIMAL(0,0) column.
Creating a DECIMAL(1,0) column instead.

- There are multiple inconsistency and incorrect way in which rw-lock
  stats are calculated.

- shared rw-lock stats:
  "rounds" counter is incremented only once for N rounds done
  in spin-cycle.

- all rw-lock stats:
  If the spin-cycle is short-circuited then attempts are re-counted.
  [If spin-cycle is interrupted, before it completes
   srv_n_spin_wait_rounds (default 30) rounds, spin_count is incremented
   to consider this. If thread resumes spin-cycle (due to unavailability
   of the locks) and is again interrupted or completed, spin_count
   is again incremented with the total count, failing to adjust the
   previous attempt increment].

- s/x rw-lock stats:
  spin_loop counter is not incremented at-all instead it is projected
  as 0 (in show engine output) and division to calculate spin-round per
  spin-loop is adjusted.
  As per the original semantics spin_loop counter should be incremented
  once per spin_loop execution.

- sx rw-lock stats:
  sx locks increments spin_loop counter but instead of incrementing it
  once for a spin_loop invocation it does it multiple times based on how
  many time spin_loop flow is repeated for same instance post os-wait.

MDEV-22503 MDB limits DECIMAL column precision to 16 doing CTAS with floor/ceil over DECIMAL(X,Y) where X > 16

The DECIMAL data type branch in Item_func_int_val::fix_length_and_dec()
incorrectly used DOUBLE-style length calculation, which resulted in
a smaller data type than the actual result of FLOOR()/CEIL() needs.

MDEV-19622 Assertion failures in
ha_partition::set_auto_increment_if_higher upon UPDATE on Aria
table

Flush LSN to system tablespace on innodb shutdown if XA is rolled back by
mariabackup.

innobase_get_charset(), innobase_get_stmt_safe(): Remove.
It is more efficient and readable to invoke thd_charset()
and thd_query_safe() directly, without a non-inlined wrapper function.