nativeClear method
Releases bridge/native-side resources tied to this listener — for example, an unregister call against a global service or a Dart-side event-handler detach.
Called by dispose before clearListeners so the event source is stopped before local references are severed: any straggler event that arrives in the window between the two calls still finds live callbacks and is delivered as it would have been, rather than silently no-oping against null fields mid-teardown.
Listeners with no native-side state may leave the body empty.
Implementation
@override
void nativeClear() {
GemKitPlatform.instance.unregisterEventHandler(pointerId);
}