Avoid using downcast<>() in ElementData::attributesIterator(), for performance reasons.
Pull request: https://github.com/WebKit/WebKit/pull/25756
Committed 275978@main (d7f01add50eb): <https://commits.webkit.org/275978@main> Reviewed commits have been landed. Closing PR #25756 and removing active labels.
<rdar://problem/124452839>