Basic implementation of tracker roles

[lyuma]

This patch exposes the name of the assigned tracker role at the beginning of the device name.

This does not expose roles being changed, or allow editable tracker bindings.

[BastiaanOlij]

Owh thats pretty cool! I don't think it's the right thing to do but I can understand why you did it this way. This ties into the action system, I'm actually pretty happy to see that it extends like this, the documentation around this is so poor.

With the latest version you should be able to just define actions for these, then bind the tracker to the right action, and then use https://github.com/GodotVR/godot-openvr-asset/wiki/OpenVR-actions#openvrpose instead of ARVRController.