add (very rough) gizmo, restructure Dart package into library, add EntityListWidget

lib/filament/widgets/filament_gesture_detector.dart

@@ -0,0 +1,93 @@
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_filament/filament/widgets/filament_gesture_detector_desktop.dart';
+import 'package:flutter_filament/filament/widgets/filament_gesture_detector_mobile.dart';
+import '../filament_controller.dart';
+
+enum GestureType { rotateCamera, panCamera, panBackground }
+
+///
+/// A widget that translates finger/mouse gestures to zoom/pan/rotate actions.
+///
+class FilamentGestureDetector extends StatelessWidget {
+  ///
+  /// The content to display below the gesture detector/listener widget.
+  /// This will usually be a FilamentWidget (so you can navigate by directly interacting with the viewport), but this is not necessary.
+  /// It is equally possible to render the viewport/gesture controls elsewhere in the widget hierarchy. The only requirement is that they share the same [FilamentController].
+  ///
+  final Widget? child;
+
+  ///
+  /// The [controller] attached to the [FilamentWidget] you wish to control.
+  ///
+  final FilamentController controller;
+
+  ///
+  /// If true, an overlay will be shown with buttons to toggle whether pointer movements are interpreted as:
+  /// 1) rotate or a pan (mobile only),
+  /// 2) moving the camera or the background image (TODO).
+  ///
+  final bool showControlOverlay;
+
+  ///
+  /// If false, gestures will not manipulate the active camera.
+  ///
+  final bool enableCamera;
+
+  ///
+  /// If false, pointer down events will not trigger hit-testing (picking).
+  ///
+  final bool enablePicking;
+
+  final void Function(ScaleStartDetails)? onScaleStart;
+  final void Function(ScaleUpdateDetails)? onScaleUpdate;
+  final void Function(ScaleEndDetails)? onScaleEnd;
+
+  const FilamentGestureDetector(
+      {Key? key,
+      required this.controller,
+      this.child,
+      this.showControlOverlay = false,
+      this.enableCamera = true,
+      this.enablePicking = true,
+      this.onScaleStart,
+      this.onScaleUpdate,
+      this.onScaleEnd})
+      : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder(
+        valueListenable: controller.hasViewer,
+        builder: (_, bool hasViewer, __) {
+          if (!hasViewer) {
+            return Container(child: child);
+          }
+          if (kIsWeb) {
+            throw Exception("TODO");
+          } else if (Platform.isLinux ||
+              Platform.isWindows ||
+              Platform.isMacOS) {
+            return FilamentGestureDetectorDesktop(
+              controller: controller,
+              child: child,
+              showControlOverlay: showControlOverlay,
+              enableCamera: enableCamera,
+              enablePicking: enablePicking,
+            );
+          } else {
+            return FilamentGestureDetectorMobile(
+                controller: controller,
+                child: child,
+                showControlOverlay: showControlOverlay,
+                enableCamera: enableCamera,
+                enablePicking: enablePicking,
+                onScaleStart: onScaleStart,
+                onScaleUpdate: onScaleUpdate,
+                onScaleEnd: onScaleEnd);
+          }
+        });
+  }
+}