FSkeletalAnimationRootMotionOffsetProvider

Wraps [UMovieSceneSkeletalAnimationSystem](API\Runtime\MovieSceneTracks\UMovieSceneSkeletalAnimationSyst-) as an [IMovieSceneRootMotionOffsetProvider](API\Editor\MovieSceneTools\IMovieSceneRootMotionOffsetProvi-) so the transform track editor can subtract root motion during auto-key.