compositor-wayland: allow to unset fullscreen

To be more symmetric with wayland_output_set_fullscreen(), implement the
xdg-shell path in wayland_output_set_windowed(). This should make it
possible to use the fullscreen key binding to toggle between a floating
window and fullscreen also under xdg-shell.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Acked-by: Daniel Stone <daniels@collabora.com>

libweston/compositor-wayland.c

@@ -873,8 +873,11 @@ wayland_output_set_windowed(struct wayland_output *output)
 
 	wayland_output_resize_surface(output);
 
-	if (output->parent.shell_surface)
+	if (output->parent.xdg_toplevel) {
+		zxdg_toplevel_v6_unset_fullscreen(output->parent.xdg_toplevel);
+	} else if (output->parent.shell_surface) {
 		wl_shell_surface_set_toplevel(output->parent.shell_surface);
+	}
 
 	return 0;
 }