This ups the core-graphics dependency and adds the ability to
convert a CGFont into a font file. The code is based on the code in
https://searchfox.org/mozilla-central/rev/7a8c667bdd2a4a32746c9862356e199627c0896d/gfx/2d/ScaledFontMac.cpp#255

We also switch to CFNumber::from to avoid breakage with the latest core-foundation