* add referenced assembly
* remove unused usings
* MA Merge Blend Tree is VRC specific
because it expects VRC style Animator Layer setup
* PruneParametersPass is VRChat specific
* fix: use FindAvatarTransformInParents() to be more cross platform
* fix MergeArmatureHook: nop logic for PhysBones if we do not dedup PhysBones
* fix AnimatorCombiner: ignore VRC components when non-VRC
btw, is AnimatorCombiner VRC specific?
* conditional compile some VRChat specific tests
* chore: refactor state machine clone logic out as a separate class
* feat: add layer priority and relative path root options to Merge Animator
* feat: add Merge Blend Tree component
* chore: adjust NDMF dependency
* docs: update merge-animator docs
* docs: merge blend tree docs
