quirks: sway does not damage surface beneath sub-surface, when unmapped

When unmapping a sub-surface, Sway <= 1.8 does not damage the surface
beneath the sub-surface.

https://github.com/swaywm/sway/issues/6960

The workaround is to manually damage the main surface. Previously,
this was done when exiting scrollback search, and after the ‘flash’
OSC. But other sub-surfaces, that may also be unmapped, did not.

This patch adds a quirk handler that does this, and calls it when:

* Exiting scrollback search
* Ending the ‘flash’ OSC
* Exiting unicode input mode
* Clearing URL labels
* Removing the scrollback position indicator

Closes #1335

terminal.c

@@ -406,11 +406,6 @@ fdm_flash(struct fdm *fdm, int fd, int events, void *data)
 
     term->flash.active = false;
     render_refresh(term);
-
-    /* Work around Sway bug - unmapping a sub-surface does not damage
-     * the underlying surface */
-    term_damage_margins(term);
-    term_damage_view(term);
     return true;
 }