WebXR Plane Detection - Semantic Label; Example;

[Maksims]

Add semantic label to XrPlane, as it is available on Quest 3.
This PR also implements ar-plane-detection example, that showcases how to track planes and build meshes for them.
It also slightly improves the way availability of plane detection is detected by using XRSession.enabledFeatures list.

This API works on mobile phones in real-time, while on Quest 3 is based on manually pre-scanned data and added features (like tables).

New APIs:

// pc.XrPlane
xrPlane.label // a string that describes a plane. If no description available it will be an empty string.
// list can be found here (not limited to): https://github.com/immersive-web/semantic-labels/blob/master/labels.json

Test link: https://examples.playcanvas.meta.space/#/xr/ar-planes-detection

I confirm I have read the contributing guidelines and signed the Contributor License Agreement.

[mvaligursky]

Very cool! Please attach a screenshot of the example.

[Maksims]

Very cool! Please attach a screenshot of the example.

Here is the example video.

789955c6d61bde1b6d6c09fa09905965.mp4