bpo-45772: socket.socket should be a class instead of a function (GH-23960)

* bpo-45772: socket.socket should be a class instead of a function

Currently `socket.socket` is documented as a function, but it is really
a class (and thus has function-like usage to construct an object). This
correction would ensure that Python projects that are interlinking
Python's documentation can properly locate `socket.socket` as a type.