bpo-32193: Convert asyncio to async/await usage (#4753)

bpo-32193: Convert asyncio to async/await usage (#4753)

* Convert asyncio/tasks.py to async/await

* Convert asyncio/queues.py to async/await

* Convert asyncio/test_utils.py to async/await

* Convert asyncio/base_subprocess.py to async/await

* Convert asyncio/subprocess.py to async/await

* Convert asyncio/streams.py to async/await

* Fix comments

* Convert asyncio/locks.py to async/await

* Convert asyncio.sleep to async def

* Add a comment

* Add missing news

* Convert stubs from AbstrctEventLoop to async functions

* Convert subprocess_shell/subprocess_exec

* Convert connect_read_pipe/connect_write_pip to async/await syntax

* Convert create_datagram_endpoint

* Convert create_unix_server/create_unix_connection

* Get rid of old style coroutines in unix_events.py

* Convert selector_events.py to async/await

* Convert wait_closed and create_connection

* Drop redundant line

* Convert base_events.py

* Code cleanup

* Drop redundant comments

* Fix indentation

* Add explicit tests for compatibility between old and new coroutines

* Convert windows event loop to use async/await

* Fix double awaiting of async function

* Convert asyncio/locks.py

* Improve docstring

* Convert tests to async/await

* Convert more tests

* Convert more tests

* Convert more tests

* Convert tests

* Improve test