sql: support record input types in plpgsql udfs

We are currently unable to support RECORD input arguments in UDFs using the PLpgSQL language. The underlying types in the RECORD need to be determined at assignment time, but in UDFs we currently determine parameter types from what is provided at function creation time. This could probably be fixed by using the resolved type of the argument after argument resolution when building the UDF. In addition, we have some issues with casting to type RECORD that may prevent the usefulness of this feature.

An example query:

```
CREATE FUNCTION f_105120(p1 RECORD)
RETURNS RECORD
STABLE
LANGUAGE PLPGSQL AS $$
BEGIN
RETURN p1;
END $$;

SELECT
col
FROM
(VALUES (f_105120(('hello':::STRING,)::RECORD)), (())) AS t (col)
ORDER BY col;
```

Jira issue: CRDB-29157
Epic CRDB-49018