[3.7] bpo-34323: Enhance IocpProactor.close() log (GH-11565)

[3.7] bpo-34323: Enhance IocpProactor.close() log (GH-11565)

* IocpProactor: prevent modification if closed (GH-11494)

* _wait_for_handle(), _register() and _unregister() methods of
  IocpProactor now raise an exception if closed
* Add "closed" to IocpProactor.__repr__()
* Simplify IocpProactor.close()

(cherry picked from commit 9b07681c09182d4b9d23cd52566a4992b8afecbb)

* bpo-34323: Enhance IocpProactor.close() log (GH-11555)

IocpProactor.close() now uses time to decide when to log: wait 1
second before the first log, then log every second. Log also the
number of seconds since close() was called.

(cherry picked from commit b1e45739d832e1e402a563c6727defda92e193b7)

* bpo-34323: Enhance IocpProactor.close() log again (GH-11563)

Add repr(self) to the log to display the number of pending overlapped
in the log.

(cherry picked from commit b91140fdb17472d03a7b7971f143c08a40fde923)