Unify display representation for `Field`

[alamb]

As @dqkqd observes:

There are parse_field and parse_list_field because we have two representation for Field:

• In Struct, Union, Map, RunEndEncoded: "a": nullable Int64
• In List types: nullable Int64, field: 'a'

I don't think having two different representation for Field is a wise choice,
but I don't change it in this PR.

Originally posted by @dqkqd in #8765 (comment)

[alamb]

Sorry was a dupe