Nearly every case where we use UChar32, it seems we can use char32_t instead.
<rdar://problem/118900819>
Pull request: https://github.com/WebKit/WebKit/pull/21026
Committed 271373@main (c3f90442cf07): <https://commits.webkit.org/271373@main> Reviewed commits have been landed. Closing PR #21026 and removing active labels.