Make sure DocumentLoader::interruptedForPolicyChangeError returns a cancellation error in all code paths
<rdar://103398404>
Pull request: https://github.com/WebKit/WebKit/pull/7682
Committed 257986@main (371162099eb7): <https://commits.webkit.org/257986@main> Reviewed commits have been landed. Closing PR #7682 and removing active labels.