Add support for WebXR

[paulisere]

The current demo implementation uses the WebVR API. This API has been deprecated and as a result, this demo does not work on some VR headsets (e.g. Meta Quest 2). The WebVR API has been replaced with the WebXR API. Re-implement the demo using this API.

[neuhaus]

@paulisere This is very cool, what would it take to add support for immersive (2d) viewing to Marzipano in general?

In particular the new Marzipano tool with import at https://github.com/tunnaduong/marzipano-importer uses the marzipano 0.10.2 marzipano.js file.