Cut instances in the Noto recipe provider

[simoncozens]

Now I've done various bits of optimisation, a good chunk of the time of a Noto build is caught up in instantiating UFOs in order to build static TTFs. I'd like to move towards cutting instances from VFs (that's what the front-end does, so it should be acceptable)...

However, this is currently draft because there are some differences between the cut instances and the UFO-instantiated builds, listed below. So we probably need a gftools-cut-instance which fixes up the problems, and use that instead of purely calling hb-subset.

• winAscent and winDescent are not updated, neither with fontTools varLib.instancer or hb-subset.
• hb-subset does not correct the macStyle and fsSelection bits for bold weights, leading to problems with style linking. (fontTools OK here)
• I got multiple .notdef glyphs with hb-subset. (fontTools OK here)
• hb-subset does not update the name table (fontTools does).

[yanone]

FWIW, I think the win metrics are not supposed to get updated. We have a FB check that complains if members of a family don't share the same win metrics.

[simoncozens]

That's GF policy, yes. But it's not OT spec. If the masters do have varying win metrics, then in general a static instance cutter should update them.