reorder items in args[] array. Instead of

  when1,then1,when2,then2,...[,case][,else]

sort them as

  [case,]when1,when2,...,then1,then2,...[,else]

in this case all items used for comparison take a continuous part
of the array and can be aggregated directly. and all items that
can be returned take a continuous part of the array and can be
aggregated directly. Old code had to copy them to a temporary
array before aggreation, and then copy back (thd->change_item_tree)
everything that was changed.

this is a 10.3 version of bf1ca14f

fil_space_for_table_exists_in_mem(): Fix a regression that was
introduced in commit 05863142
when removing fil_system.name_hash. The condition
!valid || space == fnamespace
was incorrectly replaced with !valid, instead of true.

fil_report_missing_tablespace(): Merge to the only caller.

Introduced new status variable for custom aggregate functions.

InnoDB always keeps all tablespaces in the fil_system cache.
The fil_system.LRU is only for closing file handles; the
fil_space_t and fil_node_t for all data files will remain
in main memory. Between startup to shutdown, they can only be
created and removed by DDL statements. Therefore, we can
let dict_table_t::space point directly to the fil_space_t.

dict_table_t::space_id: A numeric tablespace ID for the corner cases
where we do not have a tablespace. The most prominent examples are
ALTER TABLE...DISCARD TABLESPACE or a missing or corrupted file.

There are a few functional differences; most notably:
(1) DROP TABLE will delete matching .ibd and .cfg files,
even if they were not attached to the data dictionary.
(2) Some error messages will report file names instead of numeric IDs.

There still are many functions that use numeric tablespace IDs instead
of fil_space_t*, and many functions could be converted to fil_space_t
member functions. Also, Tablespace and Datafile should be merged with
fil_space_t and fil_node_t. page_id_t and buf_page_get_gen() could use
fil_space_t& instead of a numeric ID, and after moving to a single
buffer pool (MDEV-15058), buf_pool_t::page_hash could be moved to
fil_space_t::page_hash.

FilSpace: Remove. Only few calls to fil_space_acquire() will remain,
and gradually they should be removed.

mtr_t::set_named_space_id(ulint): Renamed from set_named_space(),
to prevent accidental calls to this slower function. Very few
callers remain.

fseg_create(), fsp_reserve_free_extents(): Take fil_space_t*
as a parameter instead of a space_id.

fil_space_t::rename(): Wrapper for fil_rename_tablespace_check(),
fil_name_write_rename(), fil_rename_tablespace(). Mariabackup
passes the parameter log=false; InnoDB passes log=true.

dict_mem_table_create(): Take fil_space_t* instead of space_id
as parameter.

dict_process_sys_tables_rec_and_mtr_commit(): Replace the parameter
'status' with 'bool cached'.

dict_get_and_save_data_dir_path(): Avoid copying the fil_node_t::name.

fil_ibd_open(): Return the tablespace.

fil_space_t::set_imported(): Replaces fil_space_set_imported().

truncate_t: Change many member function parameters to fil_space_t*,
and remove page_size parameters.

row_truncate_prepare(): Merge to its only caller.

row_drop_table_from_cache(): Assert that the table is persistent.

dict_create_sys_indexes_tuple(): Write SYS_INDEXES.SPACE=FIL_NULL
if the tablespace has been discarded.

row_import_update_discarded_flag(): Remove a constant parameter.

fsp_get_available_space_in_free_extents(): Declare the function static
in the only caller, and take const fil_space_t& as a parameter.

fil_space_get_by_name(): Remove.
(Implement differently in mariabackup.)

fil_ibd_open(): Check if the tablespace by the same ID already
exists. If it is the same name, return success, else failure.

trx_rsegf_get(), trx_undo_get_first_rec(): Change the parameter to
fil_space_t* so that fewer callers need to be adjusted.

trx_undo_free_page(): Remove the redundant parameter 'space'.

Remove the parameter page_size, and pass a dummy page size
to buf_page_get_gen() along with BUF_PEEK_IF_IN_POOL.

fil_discard_tablespace(): Merge to row_discard_tablespace()
which was the only caller.

fil_recreate_table(), fil_recreate_tablespace(),
fil_reinit_space_header_for_table(): Move the functions
to the only calling module and declare static.

fil_recreate_table(): Remove the constant parameter space_id=0,flags.

Replace index->table_name with index->table->name.

We can rely on the dict_table_t::space. All indexes of a table object
are always in the same tablespace. (For fulltext indexes, the data is
located in auxiliary tables, and these will continue to have their own
table objects, separate from the main table.)

This is a non-functional change (pure refactoring).

fsp_header_init(): Take fil_space_t* as a parameter.

Add fil_system_t::sys_space, fil_system_t::temp_space.
These will replace lookups for TRX_SYS_SPACE or SRV_TMP_SPACE_ID.

mtr_t::m_undo_space, mtr_t::m_sys_space: Remove.

mtr_t::set_sys_modified(): Remove.

fil_space_get_type(), fil_space_get_n_reserved_extents(): Remove.

fsp_header_get_tablespace_size(), fsp_header_inc_size():
Merge to the only caller, innobase_start_or_create_for_mysql().

fil_system_t::create(): Replaces fil_init(), fsp_init().

fil_system_t::close(): Replaces fil_close().

fil_system_t::max_n_open: Remove. Use srv_max_n_open_files directly.

create_table_info_t::create_table_def(): Assign the innodb_temporary
tablespace directly.

dict_build_tablespace_for_table(): Merge to the only remaining caller,
dict_build_table_def_step().

It does not hurt to delete non-existing records from SYS_TABLESPACES
and SYS_DATAFILES. Because MariaDB does not support CREATE TABLESPACE,
only the system tablespace (space_id=0) can contain multiple tables.
But, there are no entries for the system tablespace in these tables
(which actually are stored inside the system tablespace).

MariaDB differs from the upstream for "DDL-like" command. For these,
it sets binlog_format=STATEMENT for the duration of the statement.
This doesn't play well with MyRocks, which tries to prevent DML
commands with binlog_format!=ROW.

Also, if Locked_tables_list::reopen_tables() returned an error, then
close_cached_tables should propagate the error condition and not silently
consume it (it's difficult to have test coverage for this because this
error condition is rare)

MDEV-15117 Server crashes in in open_and_process_table or ASAN
heap-use-after-free in is_temporary_table upon creating/flushing
sequences.

Problem was that sequence_insert closed and reopened the like table
without proper locking.  Fixed by ensuring that the like table is
not reopened in sequence_insert

Problem was that sequence_insert closed and reopened the like table
without proper locking.  Fixed by ensuring that the like table is
not reopened in sequence_insert

SELECT queries on information_schema table will now not store data
in the temporary table for columns that are not used in the query.
This can drastically reduce memory when there are many rows involved
in a query, like using
SELECT table_name FROM information_schema.table
on a system with many tables.
The difference for the above query is about 14K per existing table.

The code works this way:
- Create a bitmap for all information_schema fields used in the query
- For BLOB and VARCHAR fields that are not use, create a Field_null field.

Remove compiler warnings in sphinx, item_sum.cc and opt_split.cc

This is needed as otherwise a lot of MyISAM tables may be marked
as crashed, depending on in which order tests are run

Renamed suite/rpl/include/rpl_sync.inc to rpl_sync_test.inc to
remove clash with include/rpl_sync.inc