OnEventInvokeStrategyPlugin broken

[mablae]

As discussed with @prolic:

https://github.com/prooph/service-bus/blob/develop/src/Plugin/InvokeStrategy/AbstractInvokeStrategy.php#L35

=> Extend the AbstractPlugin instead of the AbstractInvokeStrategy

and adjust the code to handle each listener:

$handlers = $actionEvent->getParam(EventBus::EVENT_PARAM_EVENT_LISTENERS);

foreach ($handlers as $handler) {
    $this->invoke($handler, $message);
}

=> Add testcase