FS: On Windows, use Win32 API accepting wide string to avoid issues with the file path encoding

[fzhinkin]

As it was pointed in #241 (comment), there might be issues with file paths on systems using something other than Unicode was a default encoding (for instance, it could be GB2312 on Windows with Chinese localization).

To avoid such issues, Native implementation should use Win32 calls that accepts wide strings (i.e. UTF-16 strings).