Rethink \latin-in-tate: if a font has a vrt2 feature, use it instead.

[ctrlcctrlv]

vrt2, which stands for “Vertical Alternates and Rotation”, is a common OpenType feature available in professional CJK fonts that fulfills the same function as \latin-in-tate in a much cleaner way. It doesn't suffer from any of the placement bugs that \latin-in-tate does, either. I think, if it's available for all the characters the user is trying to shape, we should use it instead.

Text shaped above is SILE typesetter! ＳＩＬＥ with vrt2 enabled.

[alerque]

Sounds good to me. I do wonder about the overhead of scanning all characters on the font before shaping each string. Perhaps it would be better to just see if the font has any support when we first load it and default to using it if if does, with of course an override available for when that isn't sufficient.

[ctrlcctrlv]

I was thinking \latin-in-tate itself would do the scan, not SILE in general.