getDisplayMedia capture should mute other tabs when starting
<rdar://problem/109898195>
<rdar://problem/109896538>
Pull request: https://github.com/WebKit/WebKit/pull/14396
Committed 264611@main (6406adae9bf2): <https://commits.webkit.org/264611@main> Reviewed commits have been landed. Closing PR #14396 and removing active labels.