effects/zoom: Schedule a fullscreen repaint if stopped zooming

On Wayland, screens are repainted independent of each other. If zooming
animation stops on one screen, other screens may still be stuck in the
zoomed state and therefore result in potential flickering. Issue a full
screen repaint when zooming stops to ensure that other screens are
repainted with "unscaled" contents.

BUG: 454407
Part-of: <!2472>