migrate some animation helper classes

lib/animations/bone_animation_data.dart

@@ -0,0 +1,16 @@
+import 'dart:typed_data';
+import 'package:vector_math/vector_math.dart';
+
+///
+/// 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].
+///
+class BoneAnimationData {
+  final String boneName;
+  final String meshName;
+  final Float32List frameData;
+  double frameLengthInMs;
+  BoneAnimationData(
+      this.boneName, this.meshName, this.frameData, this.frameLengthInMs);
+}