[Cocoa] font-family:system-ui results in totally garbled text when the user has a user-installed system font
<rdar://problem/113706205>
Pull request: https://github.com/WebKit/WebKit/pull/17210
Committed 267463@main (9de3b434f4b0): <https://commits.webkit.org/267463@main> Reviewed commits have been landed. Closing PR #17210 and removing active labels.