Enhance this object by wrapping it in an extender object.
$extender_name: The base name of the extending class. The base name will be checked against the current database connection to allow driver-specific subclasses as well, using the same logic as the query objects themselves.
Drupal\Core\Database\Query\ExtendableInterface The extender object, which now contains a reference to this object.
public function extend($extender_name);