MDEV-14959: Control over memory allocated for SP/PS

This patch adds support for controlling of memory allocation
done by SP/PS that could happen on second and following executions.
As soon as SP or PS has been executed the first time its memory root
is marked as read only since no further memory allocation should
be performed on it. In case such allocation takes place it leads to
the assert hit for invariant that force no new memory allocations
takes place as soon as the SP/PS has been marked as read only.

The feature for control of memory allocation made on behalf SP/PS
is turned on when both debug build is on and the cmake option
-DWITH_PROTECT_STATEMENT_MEMROOT is set.

The reason for introduction of the new cmake option
  -DWITH_PROTECT_STATEMENT_MEMROOT
to control memory allocation of second and following executions of
SP/PS is that for the current server implementation there are too many
places where such memory allocation takes place. As soon as all such
incorrect allocations be fixed the cmake option
 -DWITH_PROTECT_STATEMENT_MEMROOT
can be removed and control of memory allocation made on second and
following executions can be turned on only for debug build. Before
every incorrect memory allocation be fixed it makes sense to guard
the checking of memory allocation on read only memory by extra cmake
option else we would get a lot of failing test on buildbot.

Moreover, fixing of all incorrect memory allocations could take pretty
long period of time, so for introducing the feature without necessary
to wait until all places throughout the source code be fixed it makes
sense to add the new cmake option.

include/my_alloc.h

@@ -51,6 +51,10 @@ typedef struct st_mem_root
   */
   unsigned int first_block_usage;
 
+#ifdef PROTECT_STATEMENT_MEMROOT
+  int read_only;
+#endif
+
   void (*error_handler)(void);
   const char *name;
 } MEM_ROOT;