bpo-46955: Expose asyncio.base_events.Server as asyncio.Server (GH-31760)

This change aligns the documentation at https://docs.python.org/3/library/asyncio-eventloop.htmlGH-asyncio.Server
with the actual implementation

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>
(cherry picked from commit da80d6b2f3beff519cb1457d5e055168c89f7224)

Co-authored-by: Stefan Zabka <zabkaste@informatik.hu-berlin.de>