[indic] Some scripts like blwf applied to pre-base characters

...while some don't!

Improved Bengali, Devanagari, Gurmukhi, Malayalam.

Updated numbers:

BENGALI: 353732 out of 354188 tests passed. 456 failed (0.128745%)
DEVANAGARI: 707307 out of 707394 tests passed. 87 failed (0.0122987%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60732 out of 60747 tests passed. 15 failed (0.0246926%)
KANNADA: 951030 out of 951913 tests passed. 883 failed (0.0927606%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
MALAYALAM: 1048134 out of 1048334 tests passed. 200 failed (0.0190779%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271666 out of 271847 tests passed. 181 failed (0.0665816%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
[myanmar] Apply abvm/blwm
[indic] Handle Avagraha

It can come either at the end(ish!) of the syllable, or independently.
When independent, it accepts a few bits and pieces.
[indic] Don't apply presentation features across syllables

More like Uniscribe...  We still allow user-defined features to
work across syllables, but not pres,blws,abs,psts,etc.

This "regressed" Sinhala numbers by 11.  These are cases were
there's Consonant followed by Ra,Halant,ZWJ at the of text.
The Ra,Halant,ZWJ ends up forming reph, which is wrong...
But before we were also ligating that reph with the previous
consonant.  That's even more wrong.  That's also what Uniscribe
does.

Current numbers:

BENGALI: 353732 out of 354188 tests passed. 456 failed (0.128745%)
DEVANAGARI: 707307 out of 707394 tests passed. 87 failed (0.0122987%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60732 out of 60747 tests passed. 15 failed (0.0246926%)
KANNADA: 951030 out of 951913 tests passed. 883 failed (0.0927606%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
MALAYALAM: 1048140 out of 1048334 tests passed. 194 failed (0.0185056%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271655 out of 271847 tests passed. 192 failed (0.070628%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
[indic] Apply 'kern' for all scripts except for Khmer in Uniscribe mode

Seems to better match Uniscribe.

Note: NotoSansTelugu-Regular has kern feature, so this fixes most of the
positioning failures there, except for the kern pairs blocked by a
(non-)joiner, in which case we (correctly) kern, but Uniscribe doesn't.
[tests] Remove Myanmar micro-font and test
[indic] Harmless reordering of Khmer features!
[indic] If Malayalam dot-reph formed a ligature, don't move it

Rachana-0.6 implements dot-reph by ligation, so we shouldn't move it.
Uniscribe doesn't either.  Test case:

  U+0D4E,U+0D1A,U+0D4D,U+0D1A,U+0D4D
[indic] Simplify reph logic

*Shouldn't* break anything.