We don't apply them together anyway.  Should not make any difference
right now.

Lohit Devanagari has a glyph named:
u0924_u094D.half_u0930_u094D.blwf.vatu

Such it wouldn't apply to pointers accidentally.

Oops.  I broken this badly and the test suite did not notice.  That
worries me.  Have to investigate.

At this point, the GDEF glyph synthesis looks pointless.  Not that I
have many fonts without GDEF lying around.

As for mark advance zeroing when GPOS not available, that also is being
replaced by proper fallback mark positioning soon.

This concludes the Indic shape_plan work.  May do for Arabic also...

Almost done.  Need to add per-script static tables.

Hookup some Indic data to it.  More to come.

We need the font for glyph lookup during GSUB pauses in Indic shaper.
Could perhaps be avoided, but at this point, we don't mean to support
separate substitute()/position() entry points (anymore), so there is
no point in not providing the font to GSUB.

It was impossible to meaningfully use them from the outside these days.

To be moved to initial_reordering next...

Move all the logic that needs to eventually move into the indic table
into hb-ot-shape-complex-indic-private.hh.

Comes with some 10% speedup for Devanagari even!

Gives me a good 10% speedup for the Devanagari test case.  Less so
for less lookup-intensive tests.

For the Devanagari test case, the false positive rate of the GSUB digest
is 4%.

Implement two set digests, and one that combines the two.