Webxr refactor

[joshmarinacci]

WebXR bindings

Changes proposed:

• add XREffect
• add XRControls
• add xr-anchor component

[dmarcos]

Thanks! VREffect / VRControls will be gone in the next A-Frame version (see #3152). I recommend starting making a WebXRManager similar to the WebVRManager that replaces VREffect / VRControls (https://github.com/mrdoob/three.js/blob/dev/src/renderers/webvr/WebVRManager.js). WebXR is still highly experimental so I would keep it as a separate aframe-xr.js library that bundles both the WebXRManager, the webxr-polyfill and associated components. At load, the library would swap WebVRManager with the WebXRManager in the renderer: sceneEl.renderer.vr = new WebXRManager() and register the relevant components for ar scenarios.

[ngokevin]

Agreed with not tunneling down into that deep of an experimental level, and three.js has moved away from Effect/Controls, so this direction won't be viable regardless. We can discuss in an issue next time so we don't waste your efforts (unless you were planning on doing this anyways). Thanks!