From 10.4.13, the `mariadb.sys` user was created to replace `root` definers.
 - In commit 0253ea7f, definer of
   Add/DropGeometryColumn procedures was changed to `mariadb.sys`, in
   `scripts/maria_add_gis_sp.sql.in`.
   However, maria_add_gis_sp.sql only applies to new databases created by
   installation script. Databases upgraded from old versions will miss this
   change.
 - In addition, according to commit
   0d6d801e(MDEV-23102), in some scenarios
   when root user is replaced it will skip creating `mariadb.sys` user.

This commit is to update the definer from `root` to `mariadb.sys` during
upgrade. It only makes the change if the original definers are root.

Doesn't choose to execute `maria_add_gis_sp.sql` in upgrade script to
recreate the procedures is because of considering the scenarios of
MDEV-23102 that `root` user is replaced and `mariadb.sys` is not created.

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.