Add a button to element fullscreen on visionOS that enters video fullscreen
<rdar://problem/124975583>
Pull request: https://github.com/WebKit/WebKit/pull/26086
Pull request: https://github.com/WebKit/WebKit/pull/26256
Committed 276512@main (19d9df6cb358): <https://commits.webkit.org/276512@main> Reviewed commits have been landed. Closing PR #26256 and removing active labels.