Server: Command-line-specified country ID interpretation changed after switch to 3.9.0/Qt6

[hoffie]

After updating to 3.9.0 and Qt6, the country of my server changed without any changes to the config, apparently it is using Qt6 Country IDs now. I fixed it by updating to the new code in this list: https://doc.qt.io/qt-6/qlocale.html#Country-enum

Originally posted by @acerix in #2362 (comment)

If confirmed, this affects servers using our official releases on Mac and custom-built servers on other platforms (e.g. Linux with self-built binaries or distros which have switched to Qt6 such as Arch).

[hoffie]

src/main.cpp, src/server.cpp and src/serverlist.cpp don't do Qt5-to-Qt6 conversion, but it would probably be required to do so as Qt6 builds are supposed to work with Qt6 codes internally and convert from/to Qt5 codes when interacting with the outside world (network/protocol, CLI).

[hoffie]

I've confirmed this issue -- a server with country id 82 (Germany) becomes Fiji on 3.9.0/Qt6.