Update httpHeaderNameString() to return an ASCIILiteral instead of a StringView. It makes it clearer that it only returns ASCII characters and that they are "immortal".
Pull request: https://github.com/WebKit/WebKit/pull/14360
Committed 264587@main (fa601944b216): <https://commits.webkit.org/264587@main> Reviewed commits have been landed. Closing PR #14360 and removing active labels.
<rdar://problem/109892743>