FinalIK Constraints for VRChat

Requires RootMotion's Final IK:

https://assetstore.unity.com/packages/tools/animation/final-ik-14290

This is a set of two prefabs making use of FinalIK components to create a World Constraint and Rotation Constraint that both update correctly in VRChat's mirrors/cameras. Additionally, the World Constraint fixes issues with Dynamic Bones being dragged along by your root avatar on dropped/constrained objects. The README file includes a more detailed breakdown.

Inspired by the VRLabs World Constraint:

https://vrlabs.dev/item/world-constraint