[io grant] Make IO::Path.resolve set CWD to $!SPEC.dir-sep

The `self` is a bit of a nonsensical value that is still visible
to the outside via `.perl`. Setting it to .dir-sep will make it
set CWD to be the root path of the current volume.

src/core/IO/Path.pm

@@ -329,7 +329,7 @@ my class IO::Path is Cool does IO {
             }
         }
         $resolved = $sep unless nqp::chars($resolved);
-        IO::Path!new-from-absolute-path($resolved,:$!SPEC,:CWD(self));
+        IO::Path!new-from-absolute-path($resolved,:$!SPEC,:CWD($sep));
     }
 
     method parent(IO::Path:D:) {    # XXX needs work