Added the median function to the parser , it should behave as a percentile_cont function with its argument fixed to 0.5

Added fix_fields for percentile function to check the type of argument and to ensure that only numeric arguments are allowed

Additionally, allow a query with window functions to be killed by the user during
its execution.

Fixed indentation in the syntax rules for the sql_yacc.yy , also added the rules of the percentile functions to
the sql_yacc_ora.yy

made changes according to the review, mostly removing unused code and fixing code to follow the  coding conventions

  1)ER_ARGUMENT_OUT_OF_RANGE: This error is thrown if the argument of the percentile function is not in the range [0,1]
  2)ER_ARGUMENT_NOT_CONSTANT: This error is thrown if the argument of the percnetile function is not constant in the
    entire partition of the window function

Added the error ER_WRONG_TYPE_FOR_PERCENTILE_CONT, which ensures that the result type for percentile_cont is always numerical

Added the error ER_NOT_SINGLE_ELEMENT_ORDER_LIST for th percentile functions, these ensure that for the percentile
function we have the order list with exactly one element

Added the function setting_handler_for_percentile_function() for the percentile_disc function that would
set the type of the result field for percentile_disc. Percentile_cont would habe double precision result type

if we get any error during the add function call. This is currently used only for the
percentile functions

  -ER_NOT_SINGLE_ELEMENT_ORDER_LIST
  -ER_WRONG_TYPE_FOR_PERCENTILE_CONT
  -ER_ARGUMENT_NOT_CONSTANT
  -ER_ARGUMENT_OUT_OF_RANGE

Val_str function added for the percentile_disc function, as it can have result type as STRING_RESULT

Ensured that the the element in the order by clause should have a numerical time, if not throw an error

Percentile class implemented, most of the functions have the same functionalite as the percentile cont class

all the null values while calculating the number of rows in the partition

Setting handler to have the return type as that of the element by which we are ordering the partition

Check for single element in the order_list is added

Finalised the synatax and have started implementing the class for the PERCENTILE_DISC

#cmakedefine in template file might not create a #define in configured
header file.

Status variables added: Table_open_cache_hits, Table_open_cache_misses,
Table_open_cache_overflows, Table_open_cache_active_instances.

This is a 10.3 specific part of MDEV-13049.
It disables automatic sorting for
"SELECT .. FROM INFORMATION_SCHEMA.{SCHEMATA|TABLES}"
and adjusts the affected tests accordingly.

TODO: enable MDEV-13049 optimization for 10.3

MDEV-13997 Change Item_bool_rowready_func2 to cache const items at fix time rather than evaluation time

Side effect: the second debug Note in cache_temporal_4265.result disappeared.

Before this change:
- During JOIN::cache_const_exprs(),
  Item::get_cache() for Item_date_add_interval() was called.
  The data type for date_add('2001-01-01',interval 5 day) is VARCHAR,
  because the first argument is VARCHAR (not temporal).
  Item_get_cache() created Item_cache_str('2001-01-06').
- During evaluate_join_record(), get_datetime_value() was called,
  which called Item::get_date() for Item_cache_str('2001-01-06').
  This gave the second Note. Then, get_datetime_value() created
  a new cache, now Item_cache_temporal for '2001-01-06', so not
  further str_to_datetime() happened.

After this change:
- During tem_bool_rowready_func2::fix_length_and_dec(),
  Arg_comparator::set_cmp_func_datetime() is called,
  which immediately creates an instance of Item_cache_date for
  the result of date_add('2001-01-01',interval 5 day).
  So later no str_to_datetime happens any more,
  neither during JOIN::cache_const_exprs(),
  nor during evaluate_join_record().