feature(view): add WebXR support.

[gchoqueux]

Description

Add WebXR partial support.

Features added

• headset;
• stop VR session;
• Add option to scale webxr transformation;

Work for the next PR

• add VR controllers;
• fix asynchronization between MainLoop.update and vr.renderer;
• fix wrong WebXR transformation in session starting;
• fix labels are hidden
• fix realistic atmosphere is hidden

[jogarnier]

No more feedback from my side. Just take a look of the previous ones to resolve them

[Desplandis]

@mgermerie @jogarnier I added some TODOs for the "asynchronization between MainLoop.update and vr.renderer problem.

I'll open a PR to replace calls to Window#requestAnimationFrame by the three's WebGLRenderer#setAnimationLoop. The doc says that:

For WebXR projects this function must be used.

[mgermerie]

That's all good for me, except for one question on architecture : would it be possible to leave the VR button creation responsibility to user ? We would just have the sessionstart event listener in src/Renderer/WebXR.js and user would need to trigger this event with his/hers own button or three.js premade button.
The current behavior enforces user to use three.js button.

[Desplandis]

@mgermerie Following your comment, I moved the VRButton instantiation from the Core to the example.

[mgermerie]

There is no functional test on this example, but from what I remember from testing for ColladaLoader, the functional tests fail with importmap.