Creates a new `GtkPadController` that will associate events from
pad to actions.
A null pad may be provided so the controller manages all pad devices generically, it is discouraged to mix
`GtkPadController` objects with null and non-null
on the same toplevel window, as execution order is not guaranteed.
The `GtkPadController` is created with no mapped actions. In order to map pad events to actions, use [ method@Gtk.PadController.set_action_entries] or [method@Gtk.PadController.set_action].
Be aware that pad events will only be delivered to `GtkWindow`s, so adding a pad controller to any other type of widget will not have an effect.
`GActionGroup` to trigger actions from
A gdk_source_tablet_pad device, or null to handle all pads
A newly created `GtkPadController`