[HarfBuzz] Mark zeroing for East Asian scripts

[Behdad Esfahbod]

Jonathan,

Trying with sequence of U+308F,3099,308F with NotoSansJP, looks like Uniscribe
doesn't zero the mark advance but we do.  The font has bad data for this mark,
but I want to fix the logic discrepancy.

So I'll probably add a new (null-ish) shaper for HIRAGANA, KATAKANA, and HAN,
and use HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE.

WDYT?  What to call that shaper?
-- 
behdad
http://behdad.org/