WebXR, update XRHandMesh

[AdaRoseCannon]

ThreeJS has updated the XRHand Mesh to use the official model from immersive-web/webxr-input-profiles rather than the inbuilt Oculus one, in addition there have been some changes in the way hand tracking works which may be out of date.

https://github.com/mrdoob/three.js/blob/dev/examples/jsm/webxr/XRHandMeshModel.js