handle abvm/blwm for indic scripts when generating mark features

[anthrotype]

For some "indic" scripts, ufo2ft markFeatureWriters generates abvm (above mark) and blwm (below mark) features instead of mark.

The list of scripts is here:
https://github.com/googlefonts/ufo2ft/blob/d15ef8f6f235804733c6e2ea5f01f39aafb92f45/Lib/ufo2ft/featureWriters/markFeatureWriter.py#L337

To decide whether an anchor should go to abvm or blmw there's a hard-coded list of anchor names that are assigned "below" status, the rest are assumed to be "above", see:
https://github.com/googlefonts/ufo2ft/blob/d15ef8f6f235804733c6e2ea5f01f39aafb92f45/Lib/ufo2ft/featureWriters/markFeatureWriter.py#L948-L961

This is similar to #753, where the kernFeatureWriters choose the 'dist' tag instead of 'kern' for some Indic scripts.

One affected project that I stumbled upon is https://github.com/notofonts/takri
But I expect all projects containing one of the indic scripts to be also affected.