Fix a problem with fns returning tuples with Attributes

[Hoverbear]

In #410 we introduced some new sql attribute and functionality related to SQL generation.

As part of this we removed the extern_attr_tokens from pgx-utils::sql_entity_graph::PgExtern.

Changing from:

let attrs = entity_submission.unwrap().extern_attr_tokens();

to:

https://github.com/zombodb/pgx/blob/f653be4acd519827642d59533f06bd309befa608/pgx-macros/src/rewriter.rs#L228-L232

This caused pgx_utils::sql_entity_graph::pg_extern::Attribute::to_tokens to be invoked. Since it did not return what it had parsed, later when it got re-parsed for ToSqlConfig it was revealing entity graph tokens. This functionality has been fixed and these entity graph tokens now come from to_sql_entity_graph_tokens.