[Indic] Allow Consonant_Medial's after Consonant's

Mostly affects Myanmar, but also Tai Tham, Javanese, and Cham.  The
latter three are untested (no fonts!).
diff --git a/src/hb-ot-shape-complex-indic-machine.rl b/src/hb-ot-shape-complex-indic-machine.rl
index b745466..a536da5 100644
--- a/src/hb-ot-shape-complex-indic-machine.rl
+++ b/src/hb-ot-shape-complex-indic-machine.rl
@@ -55,8 +55,9 @@
 Coeng = 14;
 Repha = 15;
 Ra    = 16;
+CM    = 17;
 
-c = (C | Ra);			# is_consonant
+c = (C | Ra)CM*;		# is_consonant
 n = ((ZWNJ?.RS)? (N.N?)?);	# is_consonant_modifier
 z = ZWJ|ZWNJ;			# is_joiner
 h = H | Coeng;			# is_halant_or_coeng