[build.webkit.org] Bring up open source visionOS builders and testers
<rdar://problem/121395049>
Pull request: https://github.com/WebKit/WebKit/pull/28667
Committed 279249@main (b4e487b43196): <https://commits.webkit.org/279249@main> Reviewed commits have been landed. Closing PR #28667 and removing active labels.