Add implementation for priority for Highlight
<rdar://problem/110125853>
Pull request: https://github.com/WebKit/WebKit/pull/14879
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/40791
*** Bug 258309 has been marked as a duplicate of this bug. ***
Committed 265812@main (3b510397ce89): <https://commits.webkit.org/265812@main> Reviewed commits have been landed. Closing PR #14879 and removing active labels.