[Bug 44016] Improve path handling in Open and Save dialogs

https://bugs.winehq.org/show_bug.cgi?id=44016

--- Comment #4 from KOLANICH  ---
> - What error does wine give? I paste "C:\windows\system32" in notepad++ open and it works as expected.

In fact I worked with that system a half year ago, I just have recently
remembered that I had wanted to create a ticket. If it works, it's fine.
> - I a agree, but I'm not sure if that's planned to be possible.

What's the problem? Wine knows all the mounted windows drives so in the case of
a rootfs path it can check if any mounted windows drive path is a prefix of a
rootfs path and then replace.

4 Could you also check if everything works with shashes instead of backslashes?
(in Windows autocomplete doesn't work for that paths (but in Wine I think it
should), but they are valid).