Unicode paths don't work for embedded mke2fs on Windows

mke2fs only supports `char *`, not `wchar_t *`, so on Windows, there's no Unicode support. on Windows 10 and newer, we should be able to work around this by using the UTF-8 code page. It looks like the way to do this is to embed a manifest into the `.exe`: https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page. I don't know how to do this with Cargo yet. EDIT: To clarify, this only affects the path to the `.img` file, not anything contained within the filesystem.