Update Hands Subsystem to use XR1 2.3 hands package on Android, so MRTK3 can consume Microsoft OpenXR version 1.8.0+

[shaynie]

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

• https://github.com/MixedRealityToolkit/MixedRealityToolkit-Unity/issues/165

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Hand tracking for Android has been removed from the Microsoft OpenXR plugin 1.8.0+. We need to rework the hands subsystem to use the XRI 2.3 hands package so that Android can still build.

For the first iteration Windows should still use Microsoft OpenXR plugin directly. Android needs to be updated to use the XR1 2.2 hands package.

[shaynie]

Hand tracking for Android has been removed from the Microsoft OpenXR plugin 1.8.0+ Need to rework the hands subsystem to use the XRI 2.3 hands package so that Android can still build.