compositor: Add weston_surface_schedule_repaint() for limited repaint

compositor: Add weston_surface_schedule_repaint() for limited repaint

In cases where we know the surface bounding box doesn't change in the
next frame, we can limit redraws to only the outputs the surface is
currently on.  We could do even better by forcing the transform
update so we know where the surface will be in the next frame, but
this is a much simpler first step.