WebGLBackground: Respect autoClear in XR.

[CodyJasonBennett]

Fixed #25955

Description

Unsets forceClear when handling the WebXR environment blendmode. Noticed this while testing #26160 which breaks the backgrounds-postprocessing example.

I didn't move this into the renderer.autoClear || forceClear guard as a best effort attempt to get a correct render between successive frames when manually clearing via renderer.clear() => renderer.render() etc.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
643.9 kB (159.7 kB)	643.9 kB (159.7 kB)	-39 B

🌳 Bundle size after tree-shaking

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

Filesize dev	Filesize PR	Diff
437 kB (105.8 kB)	437 kB (105.8 kB)	-39 B

[Mugen87]

@mrxz @marwie Can you confirm that this PR fixes your use cases?

[mrxz]

This does indeed fix my use-case (which is purely VR, environment blend mode opaque).