Those might trigger the destruction of some widget that would dispose the
event controller while the event is still being handled, so keep an extra
ref on the controller during event processing.
This prevents some of our generic object implementation tests
from working with gesture objects. Instead, add g_return_if_fail
checks in all the gesture constructors.
Event controllers now auto-attach, and the GtkCapturePhase only determines
when are events dispatched, but all controllers are managed by the widget wrt
grabs.
All callers have been updated.
The propagation phase property/methods in GtkEventController are gone,
This is now set directly on the GtkWidget add/remove controller API,
which has been made private.
The only public bit now are the new functions gtk_gesture_attach() and
gtk_gesture_detach() that will use the private API underneath.
All callers have been updated.
