Fix symlink and junction detection on Python windows

[smashery]

This PR resolves #657 - use ctypes to detect whether a directory is a link (symlink or junction on Windows). This applies even to newer versions of Python 3, because it doesn't do junction point detection.

C:\Users\smash\Desktop\shells>mklink /J junction directory
Junction created for junction <<===>> directory

C:\Users\smash\Desktop\shells>"C:\Program Files\Python38\python.exe"
Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:37:02) [MSC v.1924 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.islink('junction')
False

Verify

• Run the tests over at Added new failing test for windows junction points metasploit-framework#19554
• Create some links (mkdir /D) and junctions (mkdir /J)
• Place content inside those directories (once we remove the link, the content inside it should remain)
• Use Python meterpreter on both Python2 and Python3 to rmdir the links and junctions
• Verify that the contents of the actual folder being linked to is not deleted

[adfoster-r7]

Thanks! 🎉

Not a blocker - just for visibility, we've also got automated python tests over here - which runs across more versions of Python than the framework PR setup does 👍