createAnimationClip method
Implementation
AnimationClip createAnimationClip(Animation animation, Node bindTarget) {
  final clip = AnimationClip(animation, bindTarget);
  // Record all of the unique default transforms that this AnimationClip
  // will mutate.
  for (final binding in clip._bindings) {
    _targetTransforms[binding.node] = AnimationTransforms(
      bindPose: DecomposedTransform.fromMatrix(binding.node.localTransform),
    );
  }
  _clips[animation.name] = clip;
  return clip;
}