Bump process priority during WebPageProxy::getContentsAsAttributedString() so that the app doesn't hang waiting for a reply if the view is background.
<rdar://110464974>
Pull request: https://github.com/WebKit/WebKit/pull/15894
Committed 266115@main (886fe1f3fec6): <https://commits.webkit.org/266115@main> Reviewed commits have been landed. Closing PR #15894 and removing active labels.