Create the infrastructure for planner support functions.

Rename/repurpose pg_proc.protransform as "prosupport".  The idea is
still that it names an internal function that provides knowledge to
the planner about the behavior of the function it's attached to;
but redesign the API specification so that it's not limited to doing
just one thing, but can support an extensible set of requests.

The original purpose of simplifying a function call is handled by
the first request type to be invented, SupportRequestSimplify.
Adjust all the existing transform functions to handle this API,
and rename them fron "xxx_transform" to "xxx_support" to reflect
the potential generalization of what they do.  (Since we never
previously provided any way for extensions to add transform functions,
this change doesn't create an API break for them.)

Also add DDL and pg_dump support for attaching a support function to a
user-defined function.  Unfortunately, DDL access has to be restricted
to superusers, at least for now; but seeing that support functions
will pretty much have to be written in C, that limitation is just
theoretical.  (This support is untested in this patch, but a follow-on
patch will add cases that exercise it.)

Discussion: https://postgr.es/m/15193.1548028093@sss.pgh.pa.us

src/test/modules/test_ddl_deparse/expected/create_transform.out

@@ -7,7 +7,7 @@
 -- internal and as return argument the datatype of the transform done.
 -- pl/plpgsql does not authorize the use of internal as data type.
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-    FROM SQL WITH FUNCTION varchar_transform(internal),
+    FROM SQL WITH FUNCTION varchar_support(internal),
     TO SQL WITH FUNCTION int4recv(internal));
 NOTICE:  DDL test: type simple, tag CREATE TRANSFORM
 DROP TRANSFORM FOR int LANGUAGE SQL;

src/test/modules/test_ddl_deparse/sql/create_transform.sql

@@ -8,7 +8,7 @@
 -- internal and as return argument the datatype of the transform done.
 -- pl/plpgsql does not authorize the use of internal as data type.
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-    FROM SQL WITH FUNCTION varchar_transform(internal),
+    FROM SQL WITH FUNCTION varchar_support(internal),
     TO SQL WITH FUNCTION int4recv(internal));
 
 DROP TRANSFORM FOR int LANGUAGE SQL;

src/test/regress/expected/alter_table.out

@@ -3050,10 +3050,9 @@ DETAIL:  System catalog modifications are currently disallowed.
 -- instead create in public first, move to catalog
 CREATE TABLE new_system_table(id serial primary key, othercol text);
 ALTER TABLE new_system_table SET SCHEMA pg_catalog;
--- XXX: it's currently impossible to move relations out of pg_catalog
 ALTER TABLE new_system_table SET SCHEMA public;
-ERROR:  cannot remove dependency on schema pg_catalog because it is a system object
--- move back, will be ignored -- already there
+ALTER TABLE new_system_table SET SCHEMA pg_catalog;
+-- will be ignored -- already there:
 ALTER TABLE new_system_table SET SCHEMA pg_catalog;
 ALTER TABLE new_system_table RENAME TO old_system_table;
 CREATE INDEX old_system_table__othercol ON old_system_table (othercol);

src/test/regress/expected/object_address.out

@@ -38,7 +38,7 @@ CREATE USER MAPPING FOR regress_addr_user SERVER "integer";
 ALTER DEFAULT PRIVILEGES FOR ROLE regress_addr_user IN SCHEMA public GRANT ALL ON TABLES TO regress_addr_user;
 ALTER DEFAULT PRIVILEGES FOR ROLE regress_addr_user REVOKE DELETE ON TABLES FROM regress_addr_user;
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-	FROM SQL WITH FUNCTION varchar_transform(internal),
+	FROM SQL WITH FUNCTION varchar_support(internal),
 	TO SQL WITH FUNCTION int4recv(internal));
 CREATE PUBLICATION addr_pub FOR TABLE addr_nsp.gentable;
 CREATE SUBSCRIPTION addr_sub CONNECTION '' PUBLICATION bar WITH (connect = false, slot_name = NONE);

src/test/regress/expected/oidjoins.out

@@ -809,12 +809,12 @@ WHERE	provariadic != 0 AND
 ------+-------------
 (0 rows)
 
-SELECT	ctid, protransform
+SELECT	ctid, prosupport
 FROM	pg_catalog.pg_proc fk
-WHERE	protransform != 0 AND
-	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_proc pk WHERE pk.oid = fk.protransform);
- ctid | protransform 
-------+--------------
+WHERE	prosupport != 0 AND
+	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_proc pk WHERE pk.oid = fk.prosupport);
+ ctid | prosupport 
+------+------------
 (0 rows)
 
 SELECT	ctid, prorettype

src/test/regress/expected/opr_sanity.out

@@ -453,10 +453,10 @@ WHERE proallargtypes IS NOT NULL AND
 -----+---------+-------------+----------------+-------------
 (0 rows)
 
--- Check for protransform functions with the wrong signature
+-- Check for prosupport functions with the wrong signature
 SELECT p1.oid, p1.proname, p2.oid, p2.proname
 FROM pg_proc AS p1, pg_proc AS p2
-WHERE p2.oid = p1.protransform AND
+WHERE p2.oid = p1.prosupport AND
     (p2.prorettype != 'internal'::regtype OR p2.proretset OR p2.pronargs != 1
      OR p2.proargtypes[0] != 'internal'::regtype);
  oid | proname | oid | proname 

src/test/regress/sql/alter_table.sql

@@ -1896,10 +1896,9 @@ CREATE TABLE pg_catalog.new_system_table();
 -- instead create in public first, move to catalog
 CREATE TABLE new_system_table(id serial primary key, othercol text);
 ALTER TABLE new_system_table SET SCHEMA pg_catalog;
-
--- XXX: it's currently impossible to move relations out of pg_catalog
 ALTER TABLE new_system_table SET SCHEMA public;
--- move back, will be ignored -- already there
+ALTER TABLE new_system_table SET SCHEMA pg_catalog;
+-- will be ignored -- already there:
 ALTER TABLE new_system_table SET SCHEMA pg_catalog;
 ALTER TABLE new_system_table RENAME TO old_system_table;
 CREATE INDEX old_system_table__othercol ON old_system_table (othercol);

src/test/regress/sql/object_address.sql

@@ -41,7 +41,7 @@ CREATE USER MAPPING FOR regress_addr_user SERVER "integer";
 ALTER DEFAULT PRIVILEGES FOR ROLE regress_addr_user IN SCHEMA public GRANT ALL ON TABLES TO regress_addr_user;
 ALTER DEFAULT PRIVILEGES FOR ROLE regress_addr_user REVOKE DELETE ON TABLES FROM regress_addr_user;
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-	FROM SQL WITH FUNCTION varchar_transform(internal),
+	FROM SQL WITH FUNCTION varchar_support(internal),
 	TO SQL WITH FUNCTION int4recv(internal));
 CREATE PUBLICATION addr_pub FOR TABLE addr_nsp.gentable;
 CREATE SUBSCRIPTION addr_sub CONNECTION '' PUBLICATION bar WITH (connect = false, slot_name = NONE);

src/test/regress/sql/oidjoins.sql

@@ -405,10 +405,10 @@ SELECT	ctid, provariadic
 FROM	pg_catalog.pg_proc fk
 WHERE	provariadic != 0 AND
 	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_type pk WHERE pk.oid = fk.provariadic);
-SELECT	ctid, protransform
+SELECT	ctid, prosupport
 FROM	pg_catalog.pg_proc fk
-WHERE	protransform != 0 AND
-	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_proc pk WHERE pk.oid = fk.protransform);
+WHERE	prosupport != 0 AND
+	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_proc pk WHERE pk.oid = fk.prosupport);
 SELECT	ctid, prorettype
 FROM	pg_catalog.pg_proc fk
 WHERE	prorettype != 0 AND

src/test/regress/sql/opr_sanity.sql

@@ -353,10 +353,10 @@ WHERE proallargtypes IS NOT NULL AND
         FROM generate_series(1, array_length(proallargtypes, 1)) g(i)
         WHERE proargmodes IS NULL OR proargmodes[i] IN ('i', 'b', 'v'));
 
--- Check for protransform functions with the wrong signature
+-- Check for prosupport functions with the wrong signature
 SELECT p1.oid, p1.proname, p2.oid, p2.proname
 FROM pg_proc AS p1, pg_proc AS p2
-WHERE p2.oid = p1.protransform AND
+WHERE p2.oid = p1.prosupport AND
     (p2.prorettype != 'internal'::regtype OR p2.proretset OR p2.pronargs != 1
      OR p2.proargtypes[0] != 'internal'::regtype);