support utf8mb3 char encoding fully for mysqlclient, others

support utf8mb3 char encoding fully for mysqlclient, others

Fixes to accommodate for the MariaDB 10.6 series, including backwards
incompatible changes in both the mariadb-connector Python driver (supported
on SQLAlchemy 1.4 only) as well as the native 10.6 client libraries that
are used automatically by the mysqlclient DBAPI (applies to both 1.3 and
1.4). The "utf8mb3" encoding symbol is now reported by these client
libraries when the encoding is stated as "utf8", leading to lookup and
encoding errors within the MySQL dialect that does not expect this symbol.
Updates to both the MySQL base library to accommodate for this utf8mb3
symbol being reported as well as to the test suite. Thanks to Georg Richter
for support.

Fixes: #7136
Fixes: #7115
Change-Id: I655d9d9868aef76037023d0c602b8a7c881780b0