WebXRManager: Safely check for XRWebGLBinding.

[zonkypop]

Description

When using the immersive-web-emulator XRWebGLBinding is undefined. The current code:

const useLayers = XRWebGLBinding !== undefined && 'createProjectionLayer' in XRWebGLBinding.prototype;

throws an error because it directly references XRWebGLBinding without checking if it is defined. I'm unsure whether all WebXR devices use XRWebGLBinding or if a PR would be better suited for their repo. This is a simple fix which resolves the issue when testing any of the WebXR demos using popular emulators.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	339.52 79.1	339.53 79.09	+11 B -7 B
WebGPU	490.85 136.4	490.85 136.4	+0 B +0 B
WebGPU Nodes	490.32 136.29	490.32 136.29	+0 B +0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	465.41 112.15	465.42 112.15	+11 B -6 B
WebGPU	561.43 152.1	561.43 152.1	+0 B +0 B
WebGPU Nodes	516.81 141.67	516.81 141.67	+0 B +0 B

[Mugen87]

/cc @toji