Round-trip the zwj unicode character

Rendering of sequences containing zwj is still not implemented, since it
can cause the collapse of an unbounded number of characters into a
single cell. However, kitty at least preserves the zwj by storing it as
a combining character.

kitty/unicode-data.h

@@ -1,7 +1,7 @@
 #pragma once
 #include "data-types.h"
-#define VS15 1280
-#define VS16 1281
+#define VS15 1281
+#define VS16 1282
 
 bool is_combining_char(char_type ch);
 bool is_ignored_char(char_type ch);