Add WebXR backend for ARKit.
rdar://problem/116502210
Pull request: https://github.com/WebKit/WebKit/pull/18742
Committed 269049@main (7ad679f07143): <https://commits.webkit.org/269049@main> Reviewed commits have been landed. Closing PR #18742 and removing active labels.
Reverted by https://github.com/WebKit/WebKit/pull/18852
Re-opening for pull request https://github.com/WebKit/WebKit/pull/18852
Committed 269192@main (fe0f1a1f74e7): <https://commits.webkit.org/269192@main> Reviewed commits have been landed. Closing PR #18912 and removing active labels.