ApplicationMessageReceived isn't Async

ApplicationMessageReceived isn’t Async which breaks the async flow and requires the event implementation to do .GetAwaiter().GetResult();.

Consider adding the ability to register a Func<Task> to flow the async context and also the cancellation token.

var mqttOptions = new MqttClientOptionsBuilder()
    //...
    .WithApplicationMessageReceiver(MyReceiver)  //   WithApplicationMessageReceiver(Func<MqttApplicationMessage, CancellationToken, Task>)
    //...
    .Build();

Task MyReceiver(MqttApplicationMessage message, CancellationToken cancellationToken)
{
     // Do async stuff
}

[dpsenner]

On the develop branch the ApplicationMessageReceived event is deprecated and there is an alternative and MQTTnet does now call the ReceivedApplicationMessageHandler and awaits that handler. That makes the api async, but the internals of MQTTnet are not async yet. This issue overlaps with the discussion we had in the PR #550. I now created #556 to discuss and track those changes.

[behroozbc]

hi @chkr1011 I think is feature is implemented and should close this issue