[Indic] Limit syllables to at most five consonants

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!

src/hb-ot-shape-complex-indic-machine.rl

@@ -72,9 +72,9 @@ final_halant_group = halant_group | h.ZWNJ;
 halant_or_matra_group = (final_halant_group | matra_group*);
 
 
-consonant_syllable =	Repha? (cn.halant_group)* cn A? halant_or_matra_group? syllable_tail;
-vowel_syllable =	reph? V.n? (halant_group.cn | ZWJ.cn)* halant_or_matra_group? syllable_tail;
-standalone_cluster =	reph? place_holder.n? (halant_group.cn)* halant_or_matra_group? syllable_tail;
+consonant_syllable =	Repha? (cn.halant_group){0,4} cn A? halant_or_matra_group? syllable_tail;
+vowel_syllable =	reph? V.n? (halant_group.cn | ZWJ.cn){0,4} halant_or_matra_group? syllable_tail;
+standalone_cluster =	reph? place_holder.n? (halant_group.cn){0,4} halant_or_matra_group? syllable_tail;
 other =			any;
 
 main := |*