libobs: Put obs_get_default_rect_effect back in temporarily

This function was removed even though the browser plugin was using this
function on mac, so this is being put back in temporarily while the
browser plugin is modified to remove this function.

libobs/obs.c

@@ -1360,6 +1360,13 @@ gs_effect_t *obs_get_base_effect(enum obs_base_effect effect)
 	return NULL;
 }
 
+/* DEPRECATED */
+gs_effect_t *obs_get_default_rect_effect(void)
+{
+	if (!obs) return NULL;
+	return obs->video.default_rect_effect;
+}
+
 signal_handler_t *obs_get_signal_handler(void)
 {
 	if (!obs) return NULL;