Move hash_any prototype from access/hash.h to utils/hashutils.h

... as well as its implementation from backend/access/hash/hashfunc.c to
backend/utils/hash/hashfn.c.

access/hash is the place for the hash index AM, not really appropriate
for generic facilities, which is what hash_any is; having things the old
way meant that anything using hash_any had to include the AM's include
file, pointlessly polluting its namespace with unrelated, unnecessary
cruft.

Also move the HTEqual strategy number to access/stratnum.h from
access/hash.h.

To avoid breaking third-party extension code, add an #include
"utils/hashutils.h" to access/hash.h.  (An easily removed line by
committers who enjoy their asbestos suits to protect them from angry
extension authors.)

Discussion: https://postgr.es/m/201901251935.ser5e4h6djt2@alvherre.pgsql

contrib/citext/citext.c

@@ -3,10 +3,10 @@
  */
 #include "postgres.h"
 
-#include "access/hash.h"
 #include "catalog/pg_collation.h"
 #include "utils/builtins.h"
 #include "utils/formatting.h"
+#include "utils/hashutils.h"
 #include "utils/varlena.h"
 
 PG_MODULE_MAGIC;

contrib/hstore/hstore_op.c

@@ -3,11 +3,11 @@
  */
 #include "postgres.h"
 
-#include "access/hash.h"
 #include "access/htup_details.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
 #include "utils/builtins.h"
+#include "utils/hashutils.h"
 #include "utils/memutils.h"
 
 #include "hstore.h"

contrib/pg_stat_statements/pg_stat_statements.c

@@ -61,7 +61,6 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-#include "access/hash.h"
 #include "catalog/pg_authid.h"
 #include "executor/instrument.h"
 #include "funcapi.h"
@@ -78,6 +77,7 @@
 #include "tcop/utility.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
+#include "utils/hashutils.h"
 #include "utils/memutils.h"
 
 PG_MODULE_MAGIC;

contrib/sepgsql/uavc.c

@@ -12,11 +12,11 @@
  */
 #include "postgres.h"
 
-#include "access/hash.h"
 #include "catalog/pg_proc.h"
 #include "commands/seclabel.h"
 #include "storage/ipc.h"
 #include "utils/guc.h"
+#include "utils/hashutils.h"
 #include "utils/memutils.h"
 
 #include "sepgsql.h"