Function createUtilityLayer

Create a utility layer attached to the given engine + main scene. The returned scene shares the main scene's camera so view + projection remain in sync without manual mirroring. The utility scene renders with a fresh-cleared depth buffer (so its gizmos appear on top of the main scene) while keeping NORMAL intra-layer depth testing — solid gizmo bodies (e.g. the camera-gizmo box + cylinders) occlude their own back faces correctly.