Preparations for the Big Reformat (#4228)

A few comments between imports were removed or moved to the top of the
import block, due to behavioral differences between black and isort. See
psf/black#251 for details.

In two instances @overloads at the top of the file needed to be moved
due to psf/black#1490.

stdlib/3/asyncio/events.pyi

@@ -8,11 +8,11 @@ from asyncio.protocols import BaseProtocol
 from asyncio.tasks import Task
 from asyncio.transports import BaseTransport
 from asyncio.unix_events import AbstractChildWatcher
+from _typeshed import FileDescriptorLike
+
 if sys.version_info >= (3, 7):
     from contextvars import Context
 
-from _typeshed import FileDescriptorLike
-
 _T = TypeVar('_T')
 _Context = Dict[str, Any]
 _ExceptionHandler = Callable[[AbstractEventLoop, _Context], Any]