Reduce use of Vector::uncheckedAppend() in Source/WebKit and use faster alternatives now that uncheckedAppend() is an alias to append().
Pull request: https://github.com/WebKit/WebKit/pull/18670
Committed 268921@main (0b86d6fe93fb): <https://commits.webkit.org/268921@main> Reviewed commits have been landed. Closing PR #18670 and removing active labels.
<rdar://problem/116528041>