[php-src] Issue #11815: `PDO` explicit close connection

Issue: https://github.com/php/php-src/issues/11815 Author: kocoten1992 ### Description Hi maintainer, currently the way to close PDO connection is: 1. end php script. 2. set null to reference of PDO connection and any PDO statement to make it unreachable (https://www.php.net/manual/en/pdo.connections.php). But in case of long-live php script, if one cannot keep track of all statement, it would become a problem, a quick search about this https://stackoverflow.com/questions/18277233/pdo-closing-connection. Would PHP consider add explicit close connection to PDO...