XR Trackers support

[De-Panther]

Following a discussion in the WebXR Discord,

Support for tracking of other devices than the Left/Right controllers. Body trackers, Valve trackers, keyboards, etc...

Valve/SteamVR trackers were mentioned in the past - https://github.com/immersive-web/webxr-input-profiles/issues/47 Meta Quest has a keyboard that can be tracked (not sure if developers can already get it's pose). @cabanier mentioned this OpenXR Specification https://registry.khronos.org/OpenXR/specs/1.0/man/html/XrKeyboardTrackingDescriptionFB.html

It can be a gamepad profile that only expose the name of the device(for input profiles) and pose, no need for buttons and touch sensors.

[cabanier]

This sounds like a good idea. We should come up with a solution that works across "trackers". OpenXR has an extension just for keyboard but it would be great if there was a general solution. Maybe it's sufficient if the API returns a space and some metadata for a tracker.

[msub2]

It looks like there's a provisional OpenXR extension made specifically to support Vive trackers. Could this potentially be used to support other trackers as well? It's unclear just from a quick glance if there would need to be any significant amount of "spoofing" for say, a Tundra tracker or slime tracker to read as a Vive tracker for this extension.