sql: allow RECORD-typed OUT params for routines

Postgres doesn't allow a SQL routine input argument to be defined with type `RECORD`. However, it does allow a pure OUT parameter to have that type:
```
postgres=# create function f(out x record) language sql as $$ select row(1); $$;
CREATE FUNCTION
postgres=# select f();
f
-----
(1)
(1 row)
```
Currently, CRDB correctly disallows input `RECORD` parameters, but incorrectly also disallows output `RECORD` parameters:
```
root@localhost:26257/defaultdb> create function f(out x record) language sql as $$ select row(1); $$;
ERROR: SQL functions cannot have arguments of type record
SQLSTATE: 42P13
```

Jira issue: CRDB-38355