Now that we insert dotted-circle, tests break more easily when our indic
machine breaks.

In particular, a few Devanagari tests were having sequences like
"C,H,ZWJ,N", and because of the ZWJ the Nukta does NOT get reordered to
before the Halant as the grammar used to expect...  Fixup.

Another case is as simple as "C,ZWJ,SM".

Fixes 10 out of 79 failures:

DEVANAGARI: 707325 out of 707394 tests passed. 69 failed (0.00975411%)

Brings down Khmer failures from 162 to 47.

KHMER: 299077 out of 299124 tests passed. 47 failed (0.0157125%)

Also rebaselined some of the test files that had only-inherited lines.
Removing those, the stats are:

BENGALI: 353893 out of 354188 tests passed. 295 failed (0.0832891%)
DEVANAGARI: 707315 out of 707394 tests passed. 79 failed (0.0111678%)
GUJARATI: 366438 out of 366457 tests passed. 19 failed (0.00518478%)
GURMUKHI: 60704 out of 60747 tests passed. 43 failed (0.0707854%)
KANNADA: 951042 out of 951913 tests passed. 871 failed (0.0915%)
KHMER: 299077 out of 299124 tests passed. 47 failed (0.0157125%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1047994 out of 1048334 tests passed. 340 failed (0.0324324%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271666 out of 271847 tests passed. 181 failed (0.0665816%)
TAMIL: 1091754 out of 1091754 tests passed. 0 failed (0%)
TELUGU: 970553 out of 970573 tests passed. 20 failed (0.00206064%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

Still some regressions, but some of the more egregious cases are
addressed.

No panic, we reeally insert dotted circle when it's absolutely broken.

Fixes most of the dotted-circle cases against Uniscribe. (for Devanagari
fixes 80% of them, for Khmer 70%; the rest look like Uniscribe being
really bogus...)

I had to make a decision.  Apparently Uniscribe adds one dotted circle
to each broken character.  I tried that, but that goes wrong easily with
split matras.  So I made it add only one dotted circle to an entire
broken syllable tail.  As in: "if there was a dotted circle here, this
would have formed a correct cluster."  That works better for split
stuff, and I like it more.

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

Also limit joiners.

This limits our syllable length to a constant, and is
closer to what Uniscribe does anyway.

Two Devanagari tests regressed, but who cares about tests with 20
joiners in a row?!  Devanagari at 57 (0.00821766%) now.

One Devanagari test regressed, plus 10 Malayalam (at 1545 now).

Fixed 120 Sinhala failures.  Now at 208 (0.0765136%).

Seems to be about what Uniscribe does.  Not exactly.  But close enough.
More consonants will start a new cluster.

A few scripts went way down in failures.  In particular:

  - Devanagari failures went down from 490 to 56.
  - Telugu went down from 113 to 49.

Other scripts went down slightly or didn't change.  New numbers:

BENGALI: 353908 out of 354285 tests passed. 377 failed (0.106412%)
DEVANAGARI: 693572 out of 693628 tests passed. 56 failed (0.00807349%)
GUJARATI: 366485 out of 366506 tests passed. 21 failed (0.00572978%)
GURMUKHI: 60750 out of 60809 tests passed. 59 failed (0.0970251%)
KANNADA: 950730 out of 951913 tests passed. 1183 failed (0.124276%)
KHMER: 298613 out of 299124 tests passed. 511 failed (0.170832%)
MALAYALAM: 1046881 out of 1048416 tests passed. 1535 failed (0.146411%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271333 out of 271847 tests passed. 514 failed (0.189077%)
TAMIL: 1091837 out of 1091837 tests passed. 0 failed (0%)
TELUGU: 970524 out of 970573 tests passed. 49 failed (0.00504856%)

Some of the remaining Telugu and Devanagari issues seem to be Uniscribe
eating Anusvara when placed before a non-joiner.  Ouch!

Malayalam failures go way down.  Other scripts benefitted slightly too.
Sinhala had one or two test regressions, but...

That's really what Uniscribe does, and explains a lot of pecularities of
Halant,ZWNJ before the base.

Sent Telugu from 1% failures to 0.03%.  Improved Kannada and Malayalam
slightly.  Fixed half of Bengali, and did NOT break anything!

In Sinhala, Rakar is formed by Al-Lakuna,ZWJ,Ra.  If you put that at the
end of a Consonant,Matra syllable, you get a dotted-circle from
Uniscribe.  Apparently adding a ZWJ before the Al-Lakuna "fixes" that.
And people have been encoding that sequence...  So, allow a forced
"ZWJ,Virama,ZWJ,Ra" sequence at the of syllables.

Fixes some 100 or more of Sinhala failures.  Now at 622 only (0.23%).

The sequence <ZWJ,Al-Lakuna,ZWJ> is used in Sinhala to explicitly ask
for Rakar.  Fixes two-thousand Sinhala tests.  Not many left.

Really this time.

Fixes another 18 Khmer tests.

Fixes 1 more Devanagari test!

Fixes 2 out of 560 Devanagari failures.  AND:
Fixes 1 out of 2 Tamil failures.

Refactoring Indic machin.  No semantic change.

It's a visual Repha.

Still not positioning logical Repha as occurs in Malayalam.

Another 200 Khmer failures fixed.  547 to go.  That's better than
Devanagari!

Down another 500 or so Khmer failures!

Except that there may be a ZWNJ before a Register Shifter.

Amend the syllable structure to allow a final subscripted consonant
(Coeng+C) and a final subscripted independent vowel (Coeng+V).
Fixes another 2k of Khmer failures.

No characters recategorized yet.  No semantic change.

Fixes another 6% of the Khmer failures.

So we can use them to switch default visibility to internal if desired,
and use these to make only declared symbols public.

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 is to incorporate it into GSUB/GPOS processing.

As reported by datao zhang on the mailing list.

https://www.microsoft.com/typography/otfntdev/devanot/shaping.aspx