Partially instancing CFF appears to work, but outlines don't vary

[simoncozens]

% hb-subset --variations=wght=400:900 --unicodes='*' Sans/Variable/OTF/NotoSansCJKjp-VF.otf -o regbold.otf
% shape regbold.otf abc
[gid66=0+563|gid67=1+618|gid68=2+510]

(This is correct at 400 weight, but:)

$ shape regbold.otf abc --variations=wght=900
[gid66=0+606|gid67=1+658|gid68=2+537]

Horizontal metrics have varied correctly, outlines have not.

I don't mind if it doesn't work yet, but it should give a warning or some indication to the user.

[behdad]

I thought I implemented this. Will take a look.

[behdad]

Oh nevermind. I implemented full instancing, not partial instancing IIRC. It's really complicated but doable...

@qxliu76 can you add a warning or error?