Implement AF_UNIX sockets on Windows

[slonopotamus]

See moby/moby#36442

---

This is a rebase of #98.

[AkihiroSuda]

CI is failing

[thaJeztah]

Gave CI a kick after the last push; failure is in TestUnixSocketWithOpts, but also curious if TestNewUnixSocket needs a change in constraints (currently gated by "must be root", which may need a slightly different check on Windows likely)

=== RUN   TestNewUnixSocket
    unix_socket_test.go:39: requires root
--- SKIP: TestNewUnixSocket (0.00s)
=== RUN   TestUnixSocketWithOpts
    unix_socket_test_windows.go:11: The process cannot access the file because it is being used by another process.

Also look like staticcheck is complaining because on Windows it's a stub, which, well, is the intent here 🤔

I guess a //nolint:staticcheck // Ignore SA4017, which is a stub on Windows, and has no side-effects could work

Alternatively, we could extract the whole block and have a separate Windows and Linux implementation / wrapper for l, err := net.Listen("unix", path) (on Windows skipping the umask)

That whole umask is hairy in either case 😬

[slonopotamus]

I moved PR to draft until i figure out the test failure.

[slonopotamus]

That whole umask is hairy in either case

Yes, feels like a race condition waiting to be exploited.

[slonopotamus]

Okay, I think I'm done here.

Alternatively, we could extract the whole block and have a separate Windows and Linux implementation / wrapper

Yep, I went this route.