Introduce AttributeName enumeration for all attribute names. We have a lot of code that can benefit from this enumeration to do switch statements instead of consecutive `if` checks. The new code is a bit more efficient.
Pull request: https://github.com/WebKit/WebKit/pull/12684
Committed 262929@main (7279f1496728): <https://commits.webkit.org/262929@main> Reviewed commits have been landed. Closing PR #12684 and removing active labels.
<rdar://problem/108012231>