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

lib/filament/animations/animation_data.dart

@@ -0,0 +1,61 @@
+import 'package:vector_math/vector_math_64.dart';
+
+///
+/// Specifies frame data (i.e. weights) to animate the morph targets contained in [morphTargets] under a mesh named [mesh].
+/// [data] is laid out as numFrames x numMorphTargets.
+/// Each frame is [numMorphTargets] in length, where the index of each weight corresponds to the respective index in [morphTargets].
+/// [morphTargets] must be some subset of the actual morph targets under [mesh] (though the order of these does not need to match).
+///
+class MorphAnimationData {
+  final List<String> meshNames;
+  final List<String> morphTargets;
+
+  final List<double> data;
+
+  MorphAnimationData(
+      this.meshNames, this.data, this.morphTargets, this.frameLengthInMs) {
+    assert(data.length == morphTargets.length * numFrames);
+  }
+
+  int get numMorphTargets => morphTargets.length;
+
+  int get numFrames => data.length ~/ numMorphTargets;
+
+  final double frameLengthInMs;
+
+  Iterable<double> getData(String morphName) sync* {
+    int index = morphTargets.indexOf(morphName);
+    if (index == -1) {
+      throw Exception("No data for morph $morphName");
+    }
+    for (int i = 0; i < numFrames; i++) {
+      yield data[(i * numMorphTargets) + index];
+    }
+  }
+}
+
+///
+/// Model class for bone animation frame data.
+/// To create dynamic/runtime bone animations (as distinct from animations embedded in a glTF asset), create an instance containing the relevant
+/// data and pass to the [setBoneAnimation] method on a [FilamentController].
+/// [frameData] is laid out as [locX, locY, locZ, rotW, rotX, rotY, rotZ]
+///
+class BoneAnimationData {
+  final List<String> bones;
+  final List<String> meshNames;
+  final List<List<Quaternion>> rotationFrameData;
+  final List<List<Vector3>> translationFrameData;
+  double frameLengthInMs;
+  final bool isModelSpace;
+  BoneAnimationData(this.bones, this.meshNames, this.rotationFrameData,
+      this.translationFrameData, this.frameLengthInMs,
+      {this.isModelSpace = false});
+
+  int get numFrames => rotationFrameData.length;
+
+  BoneAnimationData frame(int frame) {
+    return BoneAnimationData(bones, meshNames, [rotationFrameData[frame]],
+        [translationFrameData[frame]], frameLengthInMs,
+        isModelSpace: isModelSpace);
+  }
+}