js: Stop using ClutterContainer API

These have been long deprecated over in clutter, and (via several
vtables) simply forward the call to the equivalent ClutterActor methods

Save ourselves the hassle and just use ClutterActor methods directly

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3010>

js/ui/pointerA11yTimeout.js

@@ -116,7 +116,7 @@ export class PointerA11yTimeout {
             let [x, y] = global.get_pointer();
 
             this._pieTimer = new PieTimer();
-            Main.uiGroup.add_actor(this._pieTimer);
+            Main.uiGroup.add_child(this._pieTimer);
             Main.uiGroup.set_child_above_sibling(this._pieTimer, null);
 
             this._pieTimer.start(x, y, timeout);