Use PseudoClassChangeInvalidation everytime pictureInPictureElement changes.
<rdar://problem/103438114>
Pull request: https://github.com/WebKit/WebKit/pull/7739
Committed 257995@main (b0e1661e0d64): <https://commits.webkit.org/257995@main> Reviewed commits have been landed. Closing PR #7739 and removing active labels.