wayland: Mark opaque_region as dirty on hide

Otherwise if we hide and show a window we recreate a new surface,
breaking the compositor's association, but potentially not resend this
data for the new surface.
This matches what we do for input_region.

gdk/wayland/gdksurface-wayland.c

@@ -3009,6 +3009,7 @@ gdk_wayland_surface_hide_surface (GdkSurface *surface)
 
   impl->has_uncommitted_ack_configure = FALSE;
   impl->input_region_dirty = TRUE;
+  impl->opaque_region_dirty = TRUE;
 
   unset_transient_for_exported (surface);