Description: PFS table designated as readonly_world and truncate_world
             can be dropped even if user does not have required privilege.

Solution: Backported part of the 26136994 to MySQL 5.7. However, we can not
          unconditionally deny DROP statement because unlike MySQL 8.0,
          MySQL 5.7 requires mysql_upgrade to be able to drop PFS table and
          recreate them. This is typically done with user account with DROP
          privilege.

          After the fix,
          - all tables belonging to readonly_world category will only
          allow SELECT operation. For rest of the privileges that are
          not denied by readonly base class, depend on regular privilege
          checking.
          - all tables belonging to truncate_world category will only
          allow SELECT and TRUNCATE operations. For reset of the privileges
          that are not denied by truncate base class, depend on regular
          privilege checking.

RB: 21664