XRManager: Reset XRWebGLBinding on session end

[harryhjsh]

Related issue: #31821

Description

XRWebGLBinding can't be cached between XR sessions. Fixes #31821.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.24 79.14	338.24 79.14	+0 B +0 B
WebGPU	579.39 160.1	579.46 160.11	+67 B +8 B
WebGPU Nodes	578 159.86	578.07 159.87	+67 B +8 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	469.83 113.84	469.83 113.84	+0 B +0 B
WebGPU	649.09 175.75	649.15 175.76	+67 B +7 B
WebGPU Nodes	603.2 164.92	603.27 164.93	+67 B +8 B