backend: Add meta_cursor_renderer_force_update()

There will be times where additional updates will be needed, such
as animated cursors. We should update the texture and redraw in
that case.

https://bugzilla.gnome.org/show_bug.cgi?id=752342

src/backends/meta-cursor-renderer.c

@@ -144,6 +144,13 @@ meta_cursor_renderer_set_cursor (MetaCursorRenderer  *renderer,
   update_cursor (renderer);
 }
 
+void
+meta_cursor_renderer_force_update (MetaCursorRenderer *renderer)
+{
+  update_cursor (renderer);
+  queue_redraw (renderer);
+}
+
 void
 meta_cursor_renderer_set_position (MetaCursorRenderer *renderer,
                                    int x, int y)