Description:
Continuation of #5528 adding logic to convert the XRPose coming from WebXR into world space. Intended usage of cursor="rayOrigin: xrselect" is to place it on the a-scene (similar to rayOrigin: mouse), but can also be placed elsewhere as the logic no longer depends on the entity it is on.

Changes proposed:

• Add and remove WebXR event listeners when changing rayOrigin type to/from xrselect and when entering/leaving XR
• Convert the WebXR pose to world space accounting for any camera rig
• Handle the case no pose is available (before tracking is established or when temporarily lost)
• Fixed a bug where a selectend from a different input source would incorrectly reset the activeXRInput freezing the active input source.