add _ssl module (#11155)

Really all I needed for fixing the inheritance was _ssl._SSLContext.
But then I needed all the other stuff in _ssl, and if I was doing that
I wanted to do a thorough job of it.

Motivation was originally related to https://github.com/python/typeshed/issues/3968 ,
but we're well beyond that now, really.

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

pyproject.toml

@@ -146,6 +146,7 @@ extra-standard-library = [
     "_random",
     "_sitebuiltins",
     "_socket",
+    "_ssl",
     "_stat",
     "_thread",
     "_threading_local",