gtkwidget: Ensure touchpad events trigger the bubbling phase

gtkwidget: Ensure touchpad events trigger the bubbling phase

For all other events, we run the bubble phase deep in the specific
::motion/button-press/release/touch handlers.

For touchpad events, it doesn't make sense to use GtkWidgetClass
slots if the intended way to deal with these are gestures, so we
run the bubble phase directly from gtk_widget_event_internal().