Use std::filesysytem to remove deprecated std::codecvt_utf8_utf16

[yusuke-tokuyoshi]

std::codecvt_utf8_utf16, that was deprecated due to security reasons, is used in utf8_to_wstring. https://github.com/GPUOpen-LibrariesAndSDKs/Orochi/blob/e8da229ac37877e431ca5a512db17246992dcd6b/Orochi/OrochiUtils.cpp#L39

If utf8_to_wstring is used only for paths, we can replace these path types with std::filesystem that handles character encoding.