This adds a notification type for shaderfx so the properties editor can
be properly notified to redraw.
Another possible solution would be to also redraw the shaderfx tab
with a ND_MODIFIER update, but this solution allows us to avoid
some unecessary redraws too. There were no existing cases of
ND_OBJECT | NC_MODIFIER updates, so those cases were
removed from buttons_area_listener.
Differential Revision: https://developer.blender.org/D8159
a856de700b