Fix all warnings given by UBSAN

The 'special' cases where we disable, suppress or circumvent UBSAN are:
- ref10 source (as here we intentionally do some shifts that UBSAN
  complains about.
- x86 version of optimized int#korr() methods. UBSAN do not like unaligned
  memory access of integers.  Fixed by using byte_order_generic.h when
  compiling with UBSAN
- We use smaller thread stack with ASAN and UBSAN, which forced me to
  disable a few tests that prints the thread stack size.
- Verifying class types does not work for shared libraries. I added
  suppression in mysql-test-run.pl for this case.
- Added '#ifdef WITH_UBSAN' when using integer arithmetic where it is
  safe to have overflows (two cases, in item_func.cc).

Things fixed:
- Don't left shift signed values
  (byte_order_generic.h, mysqltest.c, item_sum.cc and many more)
- Don't assign not non existing values to enum variables.
- Ensure that bool and enum values are properly initialized in
  constructors.  This was needed as UBSAN checks that these types has
  correct values when one copies an object.
  (gcalc_tools.h, ha_partition.cc, item_sum.cc, partition_element.h ...)
- Ensure we do not called handler functions on unallocated objects or
  deleted objects.
  (events.cc, sql_acl.cc).
- Fixed bugs in Item_sp::Item_sp() where we did not call constructor
  on Query_arena object.
- Fixed several cast of objects to an incompatible class!
  (Item.cc, Item_buff.cc, item_timefunc.cc, opt_subselect.cc, sql_acl.cc,
   sql_select.cc ...)
- Ensure we do not do integer arithmetic that causes over or underflows.
  This includes also ++ and -- of integers.
  (Item_func.cc, Item_strfunc.cc, item_timefunc.cc, sql_base.cc ...)
- Added JSON_VALUE_UNITIALIZED to json_value_types and ensure that
  value_type is initialized to this instead of to -1, which is not a valid
  enum value for json_value_types.
- Ensure we do not call memcpy() when second argument could be null.

Other things:

- Changed struct st_position to an OBJECT and added an initialization
  function to it to ensure that we do not copy or use uninitialized
  members. The change to a class was also motived that we used "struct
  st_position" and POSITION randomly trough the code which was
  confusing.
- Notably big rewrite in sql_acl.cc to avoid using deleted objects.
- Changed in sql_partition to use '^' instead of '-'. This is safe as
  the operator is either 0 or 0x8000000000000000ULL.
- Added check for select_nr < INT_MAX in JOIN::build_explain() to
  avoid bug when get_select() could return NULL.
- Reordered elements in POSITION for better alignment.
- Changed sql_test.cc::print_plan() to use pointers instead of objects.
- Fixed bug in find_set() where could could execute '1 << -1'.
- Added variable have_sanitizer, used by mtr.  (This variable was before
  only in 10.5 and up).  It can now have one of two values:
  ASAN or UBSAN.
- Moved ~Archive_share() from ha_archive.cc to ha_archive.h and marked
  it virtual. This was an effort to get UBSAN to work with loaded storage
  engines. I kept the change as the new place is better.
- Added in CONNECT engine COLBLK::SetName(), to get around a wrong cast
  in tabutil.cpp.

Changes that should not be needed but had to be done to suppress warnings
from UBSAN:

- Added static_cast<<uint16_t>> around shift to get rid of a LOT of
  compiler warnings when using UBSAN.
- Had to change some '/' of 2 base integers to shift to get rid of
  some compile time warnings.

Fixes:

MDEV-25505 Assertion `old_flags == ((my_flags & 0x10000U) ? 1 : 0)
fixed (was caused by an old version if this commit).

Reviewed by:
- Json changes: Alexey Botchkov
- Charset changes in ctype-uca.c: Alexander Barkov
- InnoDB changes: Marko Mäkelä
- sql_acl.cc changes: Vicențiu Ciorbaru
- build_explain() changes: Sergey Petrunia
Temporary commit to log changes for UBSAN

sql/sql_acl.cc

@@ -6955,7 +6955,7 @@ int mysql_table_grant(THD *thd, TABLE_LIST *table_list,
 		      bool revoke_grant)
 {
   privilege_t column_priv(NO_ACL);
-  int result;
+  int result, res;
   List_iterator <LEX_USER> str_list (user_list);
   LEX_USER *Str, *tmp_Str;
   bool create_new_users=0;
@@ -7156,10 +7156,10 @@ int mysql_table_grant(THD *thd, TABLE_LIST *table_list,
                                revoke_grant))
 	result= TRUE;
     }
-    if (int res= replace_table_table(thd, grant_table,
-                                     tables.tables_priv_table().table(),
-                                     *Str, db_name, table_name,
-                                     rights, column_priv, revoke_grant))
+    if ((res= replace_table_table(thd, grant_table,
+                                  tables.tables_priv_table().table(),
+                                  *Str, db_name, table_name,
+                                  rights, column_priv, revoke_grant)))
     {
       if (res > 0)
       {
@@ -11277,7 +11277,7 @@ mysql_revoke_sp_privs(THD *thd, Grant_tables *tables, const Sp_handler *sph,
 bool mysql_revoke_all(THD *thd,  List <LEX_USER> &list)
 {
   uint counter, revoked;
-  int result;
+  int result, res;
   ACL_DB *acl_db;
   DBUG_ENTER("mysql_revoke_all");
 
@@ -11361,30 +11361,33 @@ bool mysql_revoke_all(THD *thd,  List <LEX_USER> &list)
     {
       for (counter= 0, revoked= 0 ; counter < column_priv_hash.records ; )
       {
-        const char *user,*host;
-        GRANT_TABLE *grant_table=
-          (GRANT_TABLE*) my_hash_element(&column_priv_hash, counter);
+	const char *user,*host;
+        GRANT_TABLE *grant_table= ((GRANT_TABLE*)
+                                   my_hash_element(&column_priv_hash, counter));
+
         user= grant_table->user;
         host= safe_str(grant_table->host.hostname);
 
         if (!strcmp(lex_user->user.str,user) &&
             !strcmp(lex_user->host.str, host))
-        {
-          List<LEX_COLUMN> columns;
-          /* TODO(cvicentiu) refactor to use
+	{
+	    List<LEX_COLUMN> columns;
+            /* TODO(cvicentiu) refactor replace_db_table to use
+               Db_table instead of TABLE directly. */
+	    if (replace_column_table(grant_table,
+                                     tables.columns_priv_table().table(),
+                                     *lex_user, columns, grant_table->db,
+                                     grant_table->tname, ALL_KNOWN_ACL, 1))
+              result= -1;
+
+          /* TODO(cvicentiu) refactor replace_db_table to use
              Db_table instead of TABLE directly. */
-          if (replace_column_table(grant_table,
-                                   tables.columns_priv_table().table(),
-                                   *lex_user, columns,
-                                   grant_table->db, grant_table->tname,
-                                   ALL_KNOWN_ACL, 1))
-            result= -1;
-          if (int res= replace_table_table(thd, grant_table,
-                                           tables.tables_priv_table().table(),
-                                           *lex_user,
-                                           grant_table->db, grant_table->tname,
-                                           ALL_KNOWN_ACL, NO_ACL, 1))
-          {
+	  if ((res= replace_table_table(thd, grant_table,
+                                        tables.tables_priv_table().table(),
+                                        *lex_user, grant_table->db,
+                                        grant_table->tname, ALL_KNOWN_ACL,
+                                        NO_ACL, 1)))
+	  {
             if (res > 0)
               result= -1;
             else
@@ -11397,8 +11400,8 @@ bool mysql_revoke_all(THD *thd,  List <LEX_USER> &list)
               continue;
             }
           }
-        }
-        counter++;
+	}
+	counter++;
       }
     } while (revoked);