Error down from 20% to 7%.

Yep, on Bengali now!

For dotted-circle independent clusters, Uniscribe does no Reph shaping
for the exact sequence Ra+Halant+25CC.  Which also is the only possible
sequence with 25CC at the end.

Uniscribe allows multiple Halant+Consonant after a Vowel.
Tests:
↦       * U+0905,U+094D,U+092B,U+094D,930,94d,930

Uniscribe allows up to two nuktas per consonant and one per matra. It does so
indepent of whether the consonant already has a nukta in it.  Tests:

        * U+0916,U+093C,U+0941
        * U+0959,U+093C,U+0941
        * U+0916,U+093C,U+093C,U+0941
        * U+0959,U+093C,U+093C,U+0941
        * U+0916,U+093C,U+093C,U+093C,U+0941
        * U+0959,U+093C,U+093C,U+093C,U+0941
        * 915,93c,93c,,94d,U+0916,U+093C,U+093C,U+093e,93c,93c

See comments.

This does not apply to the context matchings.

This regresses tests right now.  And we are not sure whether this is
the right thing to do for GPOS.  But we'll figure out.

Enable by setting envvar:

  HB_OT_INDIC_OPTIONS=uniscribe-bug-compatible

Plus, LeftMatra+Halant "feature".

As can be seen in: U+092B,U+093F,U+094D

Uniscribe doesn't move the Halant, we do.  And do a broken job of it now.

Needed for upcoming changes to GSUB/GPOS mask matching.

This is to incorporate it into GSUB/GPOS processing.

Not that the code makes any difference since the presence of ZWJ itself
causes the ligature to fail to match anyway.

Another 1000 down!

Yay!

Done.  I promise.

Makes debug output much more pleasant.

More to come, for APPLY, CLOSURE, etc.