examples: Fix compositor-examples

Due to the way the wlr_output API was changed, these examples would
never get a frame event to start the rendering loop. We now commit the
outputs to start it.

(cherry picked from commit 2fea2fced8)

examples/pointer.c

@@ -265,6 +265,8 @@ static void new_output_notify(struct wl_listener *listener, void *data) {
 	wlr_xcursor_manager_load(sample->xcursor_manager, output->scale);
 	wlr_xcursor_manager_set_cursor_image(sample->xcursor_manager, "left_ptr",
 		sample->cursor);
+
+	wlr_output_commit(output);
 }