Add IDN support to our static libcurl build

[ChristianBeer]

International Domain Names (Umlaut-Domains among others) may be a thing in the future. libcurl already supports libidn2 which translates the domain name into a string that can be resolved. Since we build a static version of libcurl we also need to build a static version of libidn2 too.

Currently this would need to be implemented for Windows and Mac since we don't really have a static Linux build.

[KenSharp]

In the future? IDNs have been live for a while.

[AenBleidd]

At the moment this need to be done for MacOS only since this is the only platorm we build libraries by ourselves. Need to be checked for vcpkg builds for Android, Linux and Windows if libcurl uses libidn2.