Add support for UTF-16 strings for LowPaths in FS:USER

(Bumping this comment.) This choice and conversion shouldn't be done here, it should instead be done in the storage back-end. The accepted path types and behaviour for when each one is passed differs by archive type, so an appropriate decision needs to be made there. Converting here simply loses valuable information. Similar concern for all instances of this code. I believe this is similar to the concern @bunnei is expressing.