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/cache_innodb.result

@@ -4,7 +4,7 @@ SET SESSION DEFAULT_STORAGE_ENGINE = InnoDB;
 drop table if exists t1,t2,t3;
 set @save_query_cache_size = @@global.query_cache_size;
 set GLOBAL query_cache_size = 1355776;
-flush status;
+flush global status;
 set autocommit=0;
 create table t1 (a int not null);
 insert into t1 values (1),(2),(3);
@@ -139,7 +139,7 @@ SHOW VARIABLES LIKE 'have_query_cache';
 Variable_name	Value
 have_query_cache	YES
 SET GLOBAL query_cache_size = 204800;
-flush status;
+flush global status;
 SET @@autocommit=1;
 SET SESSION DEFAULT_STORAGE_ENGINE = InnoDB;
 CREATE TABLE t2 (s1 int, s2 varchar(1000), key(s1));