[layout] Try to speed up collect_lookups some more

Barely made a dent :(.

src/hb-ot-layout-common.hh

@@ -555,6 +555,8 @@ struct Feature
 					  unsigned int *lookup_count /* IN/OUT */,
 					  unsigned int *lookup_tags /* OUT */) const
   { return lookupIndex.get_indexes (start_index, lookup_count, lookup_tags); }
+  inline void add_lookup_indexes_to (hb_set_t *lookup_indexes) const
+  { lookupIndex.add_indexes_to (lookup_indexes); }
 
   inline const FeatureParams &get_feature_params (void) const
   { return this+featureParams; }

src/hb-ot-layout.cc

@@ -828,29 +828,14 @@ hb_ot_layout_collect_lookups (hb_face_t      *face,
 			      const hb_tag_t *features,
 			      hb_set_t       *lookup_indexes /* OUT */)
 {
+  const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
+
   hb_auto_t<hb_set_t> feature_indexes;
   hb_ot_layout_collect_features (face, table_tag, scripts, languages, features, &feature_indexes);
+
   for (hb_codepoint_t feature_index = HB_SET_VALUE_INVALID;
        hb_set_next (&feature_indexes, &feature_index);)
-  {
-    unsigned int lookup_indices[32];
-    unsigned int offset, len;
-
-    offset = 0;
-    do {
-      len = ARRAY_LENGTH (lookup_indices);
-      hb_ot_layout_feature_get_lookups (face,
-					table_tag,
-					feature_index,
-					offset, &len,
-					lookup_indices);
-
-      for (unsigned int i = 0; i < len; i++)
-	lookup_indexes->add (lookup_indices[i]);
-
-      offset += len;
-    } while (len == ARRAY_LENGTH (lookup_indices));
-  }
+    g.get_feature (feature_index).add_lookup_indexes_to (lookup_indexes);
 }
 
 /**