patch 9.1.1976: Cannot define callbacks for redraw events

patch 9.1.1976: Cannot define callbacks for redraw events

Problem:  When using listeners, there is no way to run callbacks at
          specific points in the redraw cycle.
Solution: Add redraw_listener_add() and redraw_listener_remove() and
          allow specifying callbacks for redraw start and end
          (Foxe Chen).

closes: #18902

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>