Allow a "completed" or "dispatched" method to be called on the event class when event dispatching complete

[modstore]

I would like to keep some logic in my event that should be triggered after dispatching is complete and the listeners have run (or been queued).
This would be particularly useful when listeners aren't queued and they have set values against the event class, I can then act on that rather than having to do it in multiple places after the event is fired wherever the event is called.

I have done this in my own project by overriding the dispatcher dispatch() method like below, but it would be nice if this was part of the framework.

$results = parent::dispatch($event, $payload, $halt);

if ($event instanceof CompletedEventInterface) {
    $event->completed($results);
}

return $results;