[Cocoa] Add ContextualizedNSString, to allow line breaking to use Core Foundation but also work with prior context
<rdar://problem/109747545>
Pull request: https://github.com/WebKit/WebKit/pull/14278
Committed 264454@main (da000fdb0dc7): <https://commits.webkit.org/264454@main> Reviewed commits have been landed. Closing PR #14278 and removing active labels.