[coretext] Fully support user features
Based on patch from Jonathan Kew and data from Apple.
It's not working correctly though, and I suspect I'm hitting a bug in
CoreText. When I do this:
hb-shape /Library/Fonts/Zapfino.ttf ZapfinoZapfino --shaper coretext \
--features=-liga
I expect both ligatures to turn off, but only the second one does:
[Z_a_p_f_i_n_o=0+2333|Z=7+395|a=8+285|p_f=9+433|i=11+181|n=12+261|o=13+250]
whereas if I disable 'dlig' instead of 'liga', both are turned off.
Smells...
Doesn't resolve conflicting feature settings.