test(pdo_pgsql): Exclude `pdo` implicitly required by `pdo_pgsql` from `EXTENSIONS` (#16116)

Amend PDO driver-specific class names (#14069)

As suggested in https://externals.io/message/123166

Implement PDO driver-specific subclasses

RFC: https://wiki.php.net/rfc/pdo_driver_specific_subclasses
Closes GH-12804

Co-Authored-By: Danack <Danack@basereality.com>