Add XR_FB_face_tracking support

[Malcolmnixon]

This pull request adds support for the XR_FB_face_tracking extension to the Meta vendor plugin. Users can:

• Select face-tracking features of None, Optional, and Required
• Access the tracking data through the OpenXRFbFaceTrackingExtensionWrapper singleton
• Test if face-tracking is enabled by the is_enabled() method
• Get all 63x expression weights using the get_weights() method (indexed via enums)
• Get the 2x tracking confidences using the get_confidences() method (indexed via enums)

It includes a face model from https://booth.pm/en/items/5420804 which contains almost all the blend-shapes necessary to test the face-tracking feature; although the files are quite large for this.

https://github.com/GodotVR/godot_openxr_vendors/assets/1863707/7a37bb99-86f5-4136-9ba9-11e112feb1f0

[dsnopek]

Wow, this looks so cool! I'll review in depth when I have a chance :-)

[m4gr3d]

@Malcolmnixon Just to confirm, this only works on the Quest Pro, right?

[dsnopek]

In my testing, it only works on the Quest Pro. I also tried on the Quest 3, but it does nothing there - it doesn't even show the permission overlay about face tracking

[Malcolmnixon]

@Malcolmnixon Just to confirm, this only works on the Quest Pro, right?

I believe only the Quest Pro has the face-tracking cameras necessary to do this.

[m4gr3d]

@Malcolmnixon We should consider updating the implementation to use XR_FB_face_tracking2 instead.

[Malcolmnixon]

@Malcolmnixon We should consider updating the implementation to use XR_FB_face_tracking2 instead.

That will need us to update openxr to 1.0.34 first. I'll get a separate PR ready for that.