libobs: Add function to get average render time

Useful for real-time rendering statistics

libobs/obs.c

@@ -1849,6 +1849,11 @@ double obs_get_active_fps(void)
 	return obs ? obs->video.video_fps : 0.0;
 }
 
+uint64_t obs_get_average_frame_time_ns(void)
+{
+	return obs ? obs->video.video_avg_frame_time_ns : 0;
+}
+
 enum obs_obj_type obs_obj_get_type(void *obj)
 {
 	struct obs_context_data *context = obj;