docs/qapidoc: add format_type() method

docs/qapidoc: add format_type() method

This method is responsible for generating a type name for a given member
with the correct annotations for the QAPI domain. Features and enums do
not *have* types, so they return None. Everything else returns the type
name with a "?" suffix if that type is optional, and ensconced in
[brackets] if it's an array type.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-47-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>