Environment

• OS: Windows 10 64-bit
• Compiler: MSVC 2019 community edition, current update

Is your feature request related to a problem? Please describe.
Exiv2 lists libiconv as a dependency. However it's explicitly stated in the Exiv2 docs, what it's not used on windows platform (https://github.com/Exiv2/exiv2/blob/main/README.md#Dependencies).

The library libiconv is a GNU library and we do not recommend using libiconv with Exiv2 when building with Visual Studio.

Proposed solution
Remove libiconv dependency for windows platform. (add "!windows" platform condition in vcpkg.json, fix vcpkg-cmake-wrapper.cmake)

Describe alternatives you've considered
Currently build script downloads msys and other stuff to build libiconv on windows which shouldn't be used.