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/include/query_cache_partitions.inc

@@ -40,7 +40,7 @@ show create table t1;
 
 INSERT INTO t1 VALUES (1, now(), 0);
 
-flush status;
+flush global status;
 show status like "Qcache_queries_in_cache";
 show status like "Qcache_hits";
 
@@ -76,7 +76,7 @@ show create table t1;
 
 INSERT INTO t1 VALUES (1, now(), 0);
 
-flush status;
+flush global status;
 show status like "Qcache_queries_in_cache";
 show status like "Qcache_hits";
 
@@ -97,7 +97,7 @@ drop table t1;
 --echo #
 
 flush query cache;
-flush status;
+flush global status;
 
 SET GLOBAL query_cache_size=1024*1024*512;
   CREATE TABLE `t1` (