add setViewFrustumCulling, zoomDelta for gesture detector and cleanup

example/lib/main.dart

@@ -53,6 +53,7 @@ class _ExampleWidgetState extends State<ExampleWidget> {
   bool _initialized = false;
 
   bool _coneHidden = false;
+  bool _frustumCulling = true;
 
   @override
   void initState() {
@@ -251,6 +252,14 @@ class _ExampleWidgetState extends State<ExampleWidget> {
       _filamentController.moveCameraToAsset(_cube!);
     }, "Move camera to asset"));
 
+    children.add(_item(() {
+      setState(() {
+        _frustumCulling = !_frustumCulling;
+      });
+
+      _filamentController.setViewFrustumCulling(_frustumCulling);
+    }, "${_frustumCulling ? "Disable" : "Enable"} frustum culling"));
+
     return Stack(children: [
       Positioned.fill(
           bottom: 100,