[indic] Allow up to three tone marks

According to Roozbeh, there are valid combinations in Unicode
proposals for up to three.  Previously we were allowing up to two.

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

@@ -69,7 +69,7 @@ cn = c.ZWJ?.n?;
 forced_rakar = ZWJ H ZWJ Ra;
 avagraha = Avag.N?;
 matra_group = z{0,3}.M.N?.(H | forced_rakar)?;
-syllable_tail2 = (SM.SM?.ZWNJ?)? (A.A?)? VD?;
+syllable_tail2 = (SM.SM?.ZWNJ?)? A{0,3}? VD?;
 syllable_tail =  (Coeng (cn|V))? avagraha? syllable_tail2;
 place_holder = NBSP | DOTTEDCIRCLE;
 halant_group = (z?.h.(ZWJ.N?)?);