Improve performance of ligature component matching

This O(N^2) was introduced in 8b2c94c4.
Make it O(N).

src/hb-ot-layout-gsubgpos-private.hh

@@ -764,6 +764,12 @@ static inline bool match_input (hb_apply_context_t *c,
   unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
   unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
 
+  enum {
+    LIGBASE_NOT_CHECKED,
+    LIGBASE_MAY_NOT_SKIP,
+    LIGBASE_MAY_SKIP
+  } ligbase = LIGBASE_NOT_CHECKED;
+
   match_positions[0] = buffer->idx;
   for (unsigned int i = 1; i < count; i++)
   {
@@ -783,6 +789,8 @@ static inline bool match_input (hb_apply_context_t *c,
       {
         /* ...unless, we are attached to a base ligature and that base
 	 * ligature is ignorable. */
+        if (ligbase == LIGBASE_NOT_CHECKED)
+	{
 	  bool found = false;
 	  const hb_glyph_info_t *out = buffer->out_info;
 	  unsigned int j = buffer->out_len;
@@ -797,10 +805,13 @@ static inline bool match_input (hb_apply_context_t *c,
 	    j--;
 	  }
 
-	if (!found)
-	  return_trace (false);
+	  if (found && skippy_iter.may_skip (c, out[j]) == hb_apply_context_t::matcher_t::SKIP_YES)
+	    ligbase = LIGBASE_MAY_SKIP;
+	  else
+	    ligbase = LIGBASE_MAY_NOT_SKIP;
+	}
 
-	if (skippy_iter.may_skip (c, out[j]) != hb_apply_context_t::matcher_t::SKIP_YES)
+        if (ligbase == LIGBASE_MAY_NOT_SKIP)
 	  return_trace (false);
       }
     }