https://immersive-web.github.io/webxr/#xrray-interface

The XRRay interface described in the spec has changed slightly from what's implemented in Chrome, and the implementation should be updated to match the spec's definition.

Primarily, this means:
 - Renaming transformMatrix to simply matrix
 - Adding a js-visible constructor that accepts an origin and direction
 - Adding a js-visible constructor that accepts an XRRigidTransform