qapi: type 'info' as Optional[QAPISourceInfo]

qapi: type 'info' as Optional[QAPISourceInfo]

For everything typed so far, type this parameter as
Optional[QAPISourceInfo].

In the most generic case, QAPISchemaEntity's info field may be None to
represent types that come from built-in definitions. Although some
Entity types may not currently have any built-in definitions, it is not
easily possible to constrain the type except on an ad-hoc basis using
assertions.

It's easier and simpler, then, to just say it's always an Optional type.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210201193747.2169670-16-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>