window: Handle manually bubbled events

window: Handle manually bubbled events

The multipress gesture must react to either direct events on the
GtkWindow (special cased through _gtk_widget_check_handle_wm_event),
or bubbled events from child widgets. Ensure bubbled events go
through the gesture, those are fed manually to make sure events are
only handled once, in either one or other place. The implicit grab
will ensure that doesn't change mid-action.