[ot-font] Use binary search for format12 cmap subtable

src/hb-open-type-private.hh

@@ -985,6 +985,10 @@ struct GenericSortedArrayOf : GenericArrayOf<LenType, Type>
 template <typename Type>
 struct SortedArrayOf : GenericSortedArrayOf<USHORT, Type> {};
 
+/* A sorted array with a ULONG number of elements. */
+template <typename Type>
+struct LongSortedArrayOf : GenericSortedArrayOf<ULONG, Type> {};
+
 
 } /* namespace OT */
 

src/hb-ot-cmap-table.hh

@@ -264,7 +264,7 @@ struct CmapSubtableLongSegmented
   USHORT	reserved;	/* Reserved; set to 0. */
   ULONG		length;		/* Byte length of this subtable. */
   ULONG		language;	/* Ignore. */
-  LongArrayOf<CmapSubtableLongGroup>
+  LongSortedArrayOf<CmapSubtableLongGroup>
 		groups;		/* Groupings. */
   public:
   DEFINE_SIZE_ARRAY (16, groups);