Update MRTK3 to use Unity XR Hands package

[AMollis]

This issue has been migrated a new MRTK repository, and the status of this issue will now be tracked at the following location:

• Update MRTK3 to use Unity XR Hands package MixedRealityToolkit/MixedRealityToolkit-Unity#66

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Describe the problem

With Unity's XR Hands package, Unity now exposes articulates hand tracking data. MRTK3 should be update to the utilize this package.

The easiest route to create a MRTK3 HandsSubsystem that wraps XR Hands data.

Tasks

• Create a MRTK3 HandsSubsystem that wraps XR Hands XRHandSubsystem.
• Update MRTK3 samples to use new MRTK3 HandsSubsystem
• Update MRTK3 docs

[camnewnham]

+1 ! This would hugely benefit support for Quest and the looming Apple device.