[indic] Misc harmless fixes!

First, we were abusing OT_VD instead of OT_A.  Fix that
but moving OT_A in the grammar where it belongs (which
is different from what the spec says).

Also, only allow medial consonants after all other
consonants.  This doesn't affect any current character.

Finally, fix Halant attachment in presence of medial
consonants.  Again, this currently doesn't affect any
sequence.

I lied.  There's Gurmukhi U+0A75 which is Consonant_Medial.
Uniscribe allows one of those in each of these positions:
before matras, after matras and before syllable modifiers,
and after syllable modifiers!  We currently just allow
unlimited numbers of it, before matras.

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

diff --git a/src/hb-ot-shape-complex-indic-machine.rl b/src/hb-ot-shape-complex-indic-machine.rl
index f0c66c4..1c372e1 100644
--- a/src/hb-ot-shape-complex-indic-machine.rl
+++ b/src/hb-ot-shape-complex-indic-machine.rl
@@ -58,7 +58,7 @@
 CM    = 17;
 Avag  = 18;
 
-c = (C | Ra)CM*;		# is_consonant
+c = (C | Ra);			# is_consonant
 n = ((ZWNJ?.RS)? (N.N?)?);	# is_consonant_modifier
 z = ZWJ|ZWNJ;			# is_joiner
 h = H | Coeng;			# is_halant_or_coeng
@@ -67,14 +67,14 @@
 cn = c.ZWJ?.n?;
 forced_rakar = ZWJ H ZWJ Ra;
 matra_group = z{0,3}.M.N?.(H | forced_rakar)?;
-syllable_tail =  (Coeng (cn|V))? (Avag.N?)? (SM.SM?.ZWNJ?)? (VD.VD?)?;
+syllable_tail =  (Coeng (cn|V))? (Avag.N?)? (SM.SM?.ZWNJ?)? (A.A?)? VD?;
 place_holder = NBSP | DOTTEDCIRCLE;
 halant_group = (z?.h.(ZWJ.N?)?);
 final_halant_group = halant_group | h.ZWNJ;
-halant_or_matra_group = (final_halant_group | (h.ZWJ)? matra_group{0,4});
+halant_or_matra_group = (CM.CM* | final_halant_group | (h.ZWJ)? matra_group{0,4});
 
 
-consonant_syllable =	Repha? (cn.halant_group){0,4} cn A? halant_or_matra_group? syllable_tail;
+consonant_syllable =	Repha? (cn.halant_group){0,4} cn halant_or_matra_group? syllable_tail;
 vowel_syllable =	reph? V.n? (ZWJ | (halant_group.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;
 avagraha_cluster = 	Avag.N? (SM.ZWNJ?)? (VD VD?)?;

src/hb-ot-shape-complex-indic-private.hh

diff --git a/src/hb-ot-shape-complex-indic-private.hh b/src/hb-ot-shape-complex-indic-private.hh
index 552a121..cee1572 100644
--- a/src/hb-ot-shape-complex-indic-private.hh
+++ b/src/hb-ot-shape-complex-indic-private.hh
@@ -102,7 +102,7 @@
   INDIC_SYLLABIC_CATEGORY_CONSONANT_HEAD_LETTER	= OT_C,
   INDIC_SYLLABIC_CATEGORY_CONSONANT_MEDIAL	= OT_CM,
   INDIC_SYLLABIC_CATEGORY_CONSONANT_PLACEHOLDER	= OT_NBSP,
-  INDIC_SYLLABIC_CATEGORY_CONSONANT_SUBJOINED	= OT_C,
+  INDIC_SYLLABIC_CATEGORY_CONSONANT_SUBJOINED	= OT_CM,
   INDIC_SYLLABIC_CATEGORY_CONSONANT_REPHA	= OT_Repha,
   INDIC_SYLLABIC_CATEGORY_MODIFYING_LETTER	= OT_X,
   INDIC_SYLLABIC_CATEGORY_NUKTA			= OT_N,

src/hb-ot-shape-complex-indic.cc

diff --git a/src/hb-ot-shape-complex-indic.cc b/src/hb-ot-shape-complex-indic.cc
index c0ea562..a98c540 100644
--- a/src/hb-ot-shape-complex-indic.cc
+++ b/src/hb-ot-shape-complex-indic.cc
@@ -194,15 +194,15 @@
 
 
   /* The spec says U+0952 is OT_A.  However, testing shows that Uniscribe
-   * treats U+0951..U+0952 all as OT_VD.
+   * treats U+0951..U+0954 all behave similarly.
    * TESTS:
    * U+092E,U+0947,U+0952
    * U+092E,U+0952,U+0947
    * U+092E,U+0947,U+0951
    * U+092E,U+0951,U+0947
-   * */
+   */
   if (unlikely (hb_in_range<hb_codepoint_t> (u, 0x0951, 0x0954)))
-    cat = OT_VD;
+    cat = OT_A;
 
   if (unlikely (u == 0x17D1))
     cat = OT_X;
@@ -220,7 +220,7 @@
   else if (unlikely (u == 0x200C)) cat = OT_ZWNJ;
   else if (unlikely (u == 0x200D)) cat = OT_ZWJ;
   else if (unlikely (u == 0x25CC)) cat = OT_DOTTEDCIRCLE;
-  else if (unlikely (u == 0x0A71)) cat = OT_SM; /* GURMUKHI ADDAK.  More like consonant medial. like 0A75. */
+  else if (unlikely (u == 0x0A71)) cat = OT_SM; /* GURMUKHI ADDAK.  Move it to the end. */
 
   if (cat == OT_Repha) {
     /* There are two kinds of characters marked as Repha:
@@ -249,7 +249,7 @@
   {
     pos = matra_position (u, pos);
   }
-  else if (cat == OT_SM || cat == OT_VD || cat == OT_Avag)
+  else if ((FLAG (cat) & (FLAG (OT_SM) | FLAG (OT_VD) | FLAG (OT_A) | FLAG (OT_Avag))))
   {
     pos = POS_SMVD;
   }
@@ -933,6 +933,7 @@
 	for (unsigned int j = last_halant; j < i; j++)
 	  if (info[j].indic_position() != POS_SMVD)
 	    info[j].indic_position() = info[i].indic_position();
+	last_halant = end;
       }
   }