initial work to split into dart_filament and flutter_filament

flutter_filament/example/lib/example_viewport.dart

@@ -0,0 +1,32 @@
+import 'package:flutter/widgets.dart';
+import 'package:flutter_filament/flutter_filament.dart';
+
+class ExampleViewport extends StatelessWidget {
+  final FlutterFilamentPlugin? controller;
+  final EntityTransformController? entityTransformController;
+  final EdgeInsets padding;
+  final FocusNode keyboardFocusNode;
+
+  const ExampleViewport(
+      {super.key,
+      required this.controller,
+      required this.padding,
+      required this.keyboardFocusNode,
+      this.entityTransformController});
+
+  @override
+  Widget build(BuildContext context) {
+    return controller != null
+        ? Padding(
+            padding: padding,
+            child: EntityTransformMouseControllerWidget(
+                transformController: entityTransformController,
+                child: FilamentGestureDetector(
+                    showControlOverlay: true,
+                    controller: controller!,
+                    child: FilamentWidget(
+                      plugin: controller!,
+                    ))))
+        : Container();
+  }
+}