Return a string representing the path to which the symbolic link points.
If dir_fd is not None, it should be a file descriptor open to
a directory, and path should be relative; path will then be relative to
that directory.
dir_fd may not be implemented on your platform. If it is unavailable,
using it will raise a NotImplementedError.
3.2: Added support for Windows 6.0 (Vista) symbolic links.
3.3: Added the dir_fd parameter.
3.6: Accepts a path-like object on Unix.
3.8: Accepts a path-like object and a bytes object on Windows. Added support for directory junctions, and changed to return the substitution path (which typically includes \\?\ prefix) rather than the optional “print name” field that was previously returned.