Auto merge of #14618 - MortimerGoro:webvr_api, r=larsbergstrom,emilio,jdm,nox,asajeffrey,cvan

WebVR API Implementation

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WebVR API Implementation with HTC Vive support on Windows. The current implementations only enables the WebVR support on Windows. In other platforms the API is available on JavaScript but navigator.vr.getDisplays() returns an empty array. This will change when we add support for more VR providers and platforms ;)

Info about the architecture:
https://blog.mozvr.com/webvr-servo-architecture-and-latency-optimizations/
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Proprietary openvr.dll must be copied next to servo.exe in order to test on HTC Vive (https://github.com/ValveSoftware/openvr/tree/master/bin/win64) I have added some of the official WebVR samples for testing. Switch on your headset and run:

mach run tests/html/webvr/room-scale.html

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