We don't set up the multisample buffer when using WebGL1 contexts in WebXR.
rdar://109424254
Pull request: https://github.com/WebKit/WebKit/pull/13938
Committed 264838@main (d6ae2528a9f3): <https://commits.webkit.org/264838@main> Reviewed commits have been landed. Closing PR #13938 and removing active labels.