Properly support non-utf8 paths

[reduf]

It's possible to have non-utf8 paths both on Windows and on Linux.

Currently, we wouldn't be able to add them, because we can only draw UTF-8 paths. One options would be to draw paths, replacing the non-utf8 characters by the usual replacement characters while keeping under the hood the actual paths. That can get messy, because everytime the input is edited, we need to figure out which paths were removed/modified/added.

We could also replace it by a format, for instance the way you would do it with WTF-8, but that could make it harder to type. Not sure what is the proper fix here.