gspell-language.c: Remove dependency on iso-codes on Windows

Hi,

As Windows has NLS APIs built in the OS which can allow us to retrieve the locale codes, the region/country codes supported by the running system, along with the localized (translated) locale/language and region/country names, we could remove the dependency on the iso-codes package and use these Windows NLS APIs instead when we are running on Windows.

This patch attempts to update gspell-language.c to remove the iso-codes run-time dependency on Windows by using the Windows NLS APIs.

With blessings, thank you!