[10.x] Add selectResultsets to database Connection

[pistvan]

At our company many of our logic is written in SQL stored procedures, and many of them returns with multiple result sets. This PR adds a selectResultsets method to the DB facade so that the multiple result sets of these SPs can be get via a single framework call.
(Using the underlying PDO layer might be a solution but those calls does not logged by the framework.)

An example:

list($user_params, $user_notifications) = DB::selectResultsets("CALL get_user_params_and_notifications(?)", Auth::id());