win32 UNC path (in this case: wsl) is not well supported

[lxhillwind]

Suppose we have installed wsl (I use wsl1; but wsl2 should also work) with name fedora;

After "activate" it via wsl command, we can access the filesystem in UNC path \\wsl$\fedora\ (and this can be confirmed in win32 vim: just :echo globpath('\\wsl$\fedora\', '*', 0, 1).

In my system, it gives output like this (it gives / instead of \ since I have set shellslash):

['//wsl$/fedora/afs', '//wsl$/fedora/bin', '//wsl$/fedora/boot', '//wsl$/fedora/dev', '//wsl$/fedora/etc', '//wsl$/fedora/home', '//wsl$/fedora/init', '//wsl$/fedora/lib', '//wsl$/fedora/lib64', '//wsl$/fedora/lost+found', '//wsl$/fedora/media', '//wsl$/fedora/mnt', '//wsl$/fedora/opt', '//wsl$/fedora/proc', '//wsl$/fedora/root', '//wsl$/fedora/run', '//wsl$/fedora/sbin', '//wsl$/fedora/srv', '//wsl$/fedora/sys', '//wsl$/fedora/tmp', '//wsl$/fedora/usr', '//wsl$/fedora/var']

But dirvish cannot open it; with command :e \\wsl$\fedora\, output is like this:

dirvish: invalid directory: '//wsl$'

This seems to be caused by multiple reasons; but it is hard to talk about them without a context; I'd like to elaborate on them in a PR I created for this issue: #233

EDIT: I only test this in gvim / vim (not neovim); tests from others for neovim is appreciated.