Solve cross-version-upgrade testing problem induced by 1fb57af92.

Renaming varchar_transform to varchar_support had a side effect
I hadn't foreseen: the core regression tests leave around a
transform object that relies on that function, so the name
change breaks cross-version upgrade tests, because the name
used in the older branches doesn't match.

Since the dependency on varchar_transform was chosen with the
aid of a dartboard anyway (it would surely not work as a
language transform support function), fix by just choosing
a different random builtin function with the right signature.
Also add some comments explaining why this isn't horribly unsafe.

I chose to make the same substitution in a couple of other
copied-and-pasted test cases, for consistency, though those
aren't directly contributing to the testing problem.

Per buildfarm.  Back-patch, else it doesn't fix the problem.

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

@@ -5,9 +5,11 @@
 -- The function FROM SQL should have internal as single argument as well
 -- as return type. The function TO SQL should have as single argument
 -- internal and as return argument the datatype of the transform done.
--- pl/plpgsql does not authorize the use of internal as data type.
+-- We choose some random built-in functions that have the right signature.
+-- This won't actually be used, because the SQL function language
+-- doesn't implement transforms (there would be no point).
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-    FROM SQL WITH FUNCTION varchar_transform(internal),
+    FROM SQL WITH FUNCTION prsd_lextype(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

@@ -6,9 +6,11 @@
 -- The function FROM SQL should have internal as single argument as well
 -- as return type. The function TO SQL should have as single argument
 -- internal and as return argument the datatype of the transform done.
--- pl/plpgsql does not authorize the use of internal as data type.
+-- We choose some random built-in functions that have the right signature.
+-- This won't actually be used, because the SQL function language
+-- doesn't implement transforms (there would be no point).
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-    FROM SQL WITH FUNCTION varchar_transform(internal),
+    FROM SQL WITH FUNCTION prsd_lextype(internal),
     TO SQL WITH FUNCTION int4recv(internal));
 
 DROP TRANSFORM FOR int LANGUAGE SQL;

src/test/regress/expected/object_address.out

@@ -32,8 +32,10 @@ CREATE SERVER "integer" FOREIGN DATA WRAPPER addr_fdw;
 CREATE USER MAPPING FOR regtest_addr_user SERVER "integer";
 ALTER DEFAULT PRIVILEGES FOR ROLE regtest_addr_user IN SCHEMA public GRANT ALL ON TABLES TO regtest_addr_user;
 ALTER DEFAULT PRIVILEGES FOR ROLE regtest_addr_user REVOKE DELETE ON TABLES FROM regtest_addr_user;
+-- this transform would be quite unsafe to leave lying around,
+-- except that the SQL language pays no attention to transforms:
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-	FROM SQL WITH FUNCTION varchar_transform(internal),
+	FROM SQL WITH FUNCTION prsd_lextype(internal),
 	TO SQL WITH FUNCTION int4recv(internal));
 -- test some error cases
 SELECT pg_get_object_address('stone', '{}', '{}');

src/test/regress/sql/object_address.sql

@@ -36,8 +36,10 @@ CREATE SERVER "integer" FOREIGN DATA WRAPPER addr_fdw;
 CREATE USER MAPPING FOR regtest_addr_user SERVER "integer";
 ALTER DEFAULT PRIVILEGES FOR ROLE regtest_addr_user IN SCHEMA public GRANT ALL ON TABLES TO regtest_addr_user;
 ALTER DEFAULT PRIVILEGES FOR ROLE regtest_addr_user REVOKE DELETE ON TABLES FROM regtest_addr_user;
+-- this transform would be quite unsafe to leave lying around,
+-- except that the SQL language pays no attention to transforms:
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-	FROM SQL WITH FUNCTION varchar_transform(internal),
+	FROM SQL WITH FUNCTION prsd_lextype(internal),
 	TO SQL WITH FUNCTION int4recv(internal));
 
 -- test some error cases