`print_schema` in definition order

`print_schema` sort types alphabetically, which is nice for reference...

But when "learning" a new schema its probably best to read the schema in the order it was defined (get information from python source code).

Start by locating the Python implementation of `print_schema` and its tests, then inspect where type ordering is applied. Confirm the current alphabetical behavior and define completion as preserving the schema's definition order when printing while retaining the existing reference output behavior where appropriate.

Scritto dal modello di indicizzazione a partire dal testo della issue.