New header varatt.h split off from postgres.h

This new header contains all the variable-length data types support
(TOAST support) from postgres.h, which isn't needed by large parts of
the backend code.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/ddcce239-0f29-6e62-4b47-1f8ca742addf%40enterprisedb.com

src/backend/utils/adt/tsquery.c

@@ -23,6 +23,7 @@
 #include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/pg_crc.h"
+#include "varatt.h"
 
 /* FTS operator priorities, see ts_type.h */
 const int	tsearch_op_priority[OP_COUNT] =