Adding HTC tracker support

[BastiaanOlij]

This adds supports for Vive trackers to our OpenXR implementation.

The work in this PR is finished however we are waiting on a fix in SteamVR to be made official. Merging this will break tracking on the current SteamVR even if HTC trackers are not used. You can test this PR using the current SteamVR beta.

HTC trackers are small tracked devices that can track arbitrary locations. You can attach a tracker to peripheral like a gun or keyboard and track its location in space, or you can attach one or more trackers to set locations on your body to enable full body tracking. For this purpose it is important that you pair all the trackers in SteamVR and then identify the usage of each tracker.

This you do by opening the menu in your SteamVR status window and selecting Settings. In the settings window go to Controllers and then MANAGE TRACKERS. A dialog similar to the following will open up:

In this screenshot only one tracker is active and it is identified as tracking the location of a keyboard.

In Godot you need to make sure the action map is setup, if you're using the default action map but have an older version, just delete it and once you run your project an updated map is created. Else you need to manually add the entries:

You can add an XRController3D node for the tracker underneath your XROrigin3D node like so:

Note how in the inspector the tracker is set to the correct input path, in our case /user/vive_tracker_htcx/role/keyboard. All the possible trackers roles are now available in the dropdown. Just add controller nodes for each tracker you wish to support.

In the example we're simply showing a mesh of the tracker body:

A demo project showcasing this functionality can be found here: BastiaanOlij/godot4_openxr_demo#6

[BastiaanOlij]

@akien-mga not sure if there is anyone who can review this, but from my part this is ready to be merged.

[akien-mga]

Seems good.

[akien-mga]

Thanks!