Part#2 (final): rewritting the code to pass the correct enum_sp_aggregate_type
to the sp_head constructor, so sp_head never changes its aggregation type
later on. The grammar has been simplified and defragmented.
This allowed to check aggregate specific instructions right after
a routine body has been scanned, by calling new LEX methods:
  sp_body_finalize_{procedure|function|trigger|event}()

Moving some C++ code from *.yy to a few new helper methods in LEX.

Part#1: moving opt_if_not_exists from "sf_tail" and "sp_tail" to "create".

Call desync_and_pause() and resync_and_resume() only if state is s_synced.

After-merge fix for MDEV-18333 Slow_queries count doesn't increase when slow_query_log is turned off

Do not build range filters with detected impossible WHERE.
Anyway conditions cannot be used anymore to extract ranges for filters.

Right argument of Item_in_optimizer can not be cast to Item_in_subselect in invisible mode.

thd->lex->m_sql_cmd was not cleared between queries.
log_slow_query() could crash (when running mtr --ps) because of this.

slave_list was used to provide data for SHOW SLAVE HOSTS and
Slaves_connected status variable.

Introduced binlog_dump_thread_count which is exposed via Slaves_connected
(replaces slave_list.records).

Store Slave_info on THD and access it by iterating server_threads
(replaces slave_list).

Added:
THD::slave_info
binlog_dump_thread_count
show_slave_hosts_callback()

Removed:
slave_list
SLAVE_LIST_CHUNK
SLAVE_ERRMSG_SIZE
slave_list_key()
slave_info_free()
init_slave_list()
end_slave_list()
all_slave_list_mutexes
init_all_slave_list_mutexes()
key_LOCK_slave_list
LOCK_slave_list

Moved:
SLAVE_INFO -> Slave_info
register_slave() -> THD::register_slave()
unregister_slave() -> THD::unregister_slave()

Also removed redundant end_slave() from close_connections(): it is called
again soon afterwards by clean_up().

Pre-requisite for clean MDEV-18450 solution.

I know no test case for this bug in 10.1. So a test case will be
committed separately in 10.2

fts_reset_get_doc(): properly initialize fts_get_doc_t::cache

fts_fetch_index_words(): Restore the initialization len=0.
The test innodb_fts.create in 10.2 would end up in an infinite loop
if this assignment is removed, because a following iteration of the
while() loop would assign zip->zp->avail_in=len with the original value
instead of the 0 that was reset in the previous iteration.

Fix the warnings issued by GCC 8 -Wstringop-truncation
and -Wstringop-overflow in InnoDB and XtraDB.

This work is motivated by Jan Lindström. The patch mainly differs
from his original one as follows:

(1) We remove explicit initialization of stack-allocated string buffers.
The minimum amount of initialization that is needed is a terminating
NUL character.
(2) GCC issues a warning for invoking strncpy(dest, src, sizeof dest)
because if strlen(src) >= sizeof dest, there would be no terminating
NUL byte in dest. We avoid this problem by invoking strncpy() with
a limit that is 1 less than the buffer size, and by always writing
NUL to the last byte of the buffer.
(3) We replace strncpy() with memcpy() or strcpy() in those cases
when the result is functionally equivalent.

Note: fts_fetch_index_words() never deals with len==UNIV_SQL_NULL.
This was enforced by an assertion that limits the maximum length
to FTS_MAX_WORD_LEN. Also, the encoding that InnoDB uses for
the compressed fulltext index is not byte-order agnostic, that is,
InnoDB data files that use FULLTEXT INDEX are not portable between
big-endian and little-endian systems.

row_merge_create_fts_sort_index(): Initialize dict_col_t.

This fixes an access to uninitialized dict_col_t::ind when a debug
assertion in MariaDB 10.4 invokes is_dropped() in
rec_get_converted_size_comp_prefix_low(). Older MariaDB versions
seem to be unaffected by the uninitialized values, but it should
not hurt to initialize everything.

FIXME: Properly resolve conflicts between MDEV-18883
and MDEV-7742/MDEV-8305, and record the correct result for
main.log_slow

Do not init lex before choosing main select.

If a splittable materialized derived table / view T is used in a inner nest
of an outer join with impossible ON condition then T is marked as a
constant table. Yet the execution plan to build T is still searched for
in spite of the fact that is not needed. So it should be set.

Lesson learned: A HA_TOPTION_SYSVAR that is bound to
MYSQL_THDVAR_UINT does not have the type uint, but ulonglong.

Only starting with MariaDB 10.3.8 (MDEV-16365), InnoDB can actually
handle ALTER IGNORE TABLE correctly when introducing a NOT NULL
attribute to a column that contains a NULL value. Between
MariaDB Server 10.0 and 10.2, we would incorrectly return an error
for ALTER IGNORE TABLE when the column contains a NULL value.

MDEV-18806 Synchronize ALTER TABLE EXCHANGE PARTITION and PURGE grammar in sql_yacc.yy and sql_yacc_ora.yy

Timeout values in galera_2x3nodes.cnf made cluster startup
unreliable. Tweaked timeout values for more reliable cluster start.

Fixed restart_parameters in galera_sr_mysqldump_sst.

With wsrep_gtid_mode=ON, the appropriate commit hooks were not
called in all cases for applied streaming transactions.

As a fix, removed all special handling of commit order critical
section from Wsrep_high_priority_service and Wsrep_storage_service.
Now commit order critical section is always entered in ha_commit_trans().

Check for wsrep_run_commit_hook is now done in handler.cc, log.cc.
This makes it explicit that the transaction is an active wsrep
transaction which must go through commit hooks.

The test is based in the testcase attached in Jira MDEV.

don't do anything special for stored generated columns
in MyISAM repair code.

add an assert that if there are virtual indexed columns, they
_must_ be beyond the file->s->base.reclength boundary

after mysql_real_data_home was updated in get_options()

* fix CRL tests to work
* regenerate certificates to be at least 2048 bit
  (fixes buster and rhel8 in buildbot)
* update generate-ssl-cert.sh to generate crl files
* make all SSL tests to use certificates generated
  in generate-ssl-cert.sh, remove unused certificates

Backport from 10.4 9c60535f