Registry class to keep track of all IClippers that exist in the scene.
This is used during the CanvasUpdate loop to cull clippable elements. The clipping is called after layout, but before Graphic update.
| instance | Singleton instance. |
| Cull | Perform the clipping on all registered IClipper. |
| Register | Register an IClipper. |
| Unregister | Unregister an IClipper. |