[aat] Provide a way to disable `trak` and other AAT features

[drott]

Spun off from #1263 (comment)

We need a way to disable AAT features, such as trak.

#1296 is an initial PR going into this direction.

[drott]

Works for me, thanks!

https://roettsch.es/chancery_no_trak.txt
https://roettsch.es/chancery_no_trak.png

[drott]

Is my understanding correct that additional features inside morx or kerx can be controlled using feature arguments, according to the existing mappings that are now stored in hb-aat-layout.cc?

[behdad]

That's not hooked up yet, no.

I can look into it. Though probably only for whole buffer, not ranges.

[drott]

Ok, then let's reopen this. For whole buffer would be sufficient for Chrome.