Qt: Unversioned "freeciv-qt-client" settings
Qt-client seems to handle settings past-client-common-options mechanisms in fc_client::read_settings(). That uses QSettings named "freeciv-qt-client". This setup has the same problems as the shortcuts stuff.
The minimum I would want to S3_1 is have versioning for the QSettings the way we have for shortcuts: https://www.hostedredmine.com/issues/856551
That would allow us to have its content in S3_1 different from what we had in S3_0 -> dependency of #44391 and #44864