[Cocoa] Use kCTFontVariationAxesAttribute where we can
<rdar://problem/104066949>
Pull request: https://github.com/WebKit/WebKit/pull/8443
Committed 258809@main (9bdb0a69c53e): <https://commits.webkit.org/258809@main> Reviewed commits have been landed. Closing PR #8443 and removing active labels.