Avoid doing event-related work for CSS animation events when no event listener is registered.
Pull request: https://github.com/WebKit/WebKit/pull/12023
Committed 262231@main (f3a4982bb1a7): <https://commits.webkit.org/262231@main> Reviewed commits have been landed. Closing PR #12023 and removing active labels.
<rdar://problem/107329918>