MDEV-33145 Add FLUSH GLOBAL STATUS

- FLUSH GLOBAL STATUS now resets most global_status_vars.
  At this stage, this is mainly to be used for testing.
- FLUSH SESSION STATUS added as an alias for FLUSH STATUS.
- FLUSH STATUS does not require any privilege (before required RELOAD).
- FLUSH GLOBAL STATUS requires RELOAD privilege.
- All global status reset moved to FLUSH GLOBAL STATUS.
- Replication semisync status variables are now reset by
  FLUSH GLOBAL STATUS.
- In test cases, the only changes are:
  - Replace FLUSH STATUS with FLUSH GLOBAL STATUS
  - Replace FLUSH STATUS with FLUSH STATUS; FLUSH GLOBAL STATUS.
    This was only done in a few tests where the test was using SHOW STATUS
    for both local and global variables.
- Uptime_since_flush_status is now always provided, independent if
  ENABLED_PROFILING is enabled when compiling MariaDB.
- @@global.Uptime_since_flush_status is reset on FLUSH GLOBAL STATUS
  and @@session.Uptime_since_flush_status is reset on FLUSH SESSION STATUS.
- When connected, @@session.Uptime_since_flush_status is set to 0.

mysql-test/main/subselect_no_exists_to_in.result

@@ -7009,6 +7009,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Using join buffer (flat, BNL join)
 3	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	2	
 flush status;
+flush global status;
 SELECT
 (SELECT MIN(b) FROM t1, t2
 WHERE b = a AND (b = alias1.b OR EXISTS (SELECT * FROM t3))) AS m
@@ -7051,6 +7052,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Using join buffer (flat, BNL join)
 3	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	2	
 flush status;
+flush global status;
 SELECT
 (SELECT MIN(b) FROM t1, t2
 WHERE b = a AND (b = alias1.b OR EXISTS (SELECT * FROM t3))) AS m