channel method
Returns an optional AsyncTaskChannel for communication with the task.
Implementation
FutureOr<AsyncTaskChannel?> channel() {
if (_channelResolved) return _channelInstance;
var waitingChannelToResolve = _waitingChannelToResolve;
waitingChannelToResolve ??= _waitingChannelToResolve = Completer();
return waitingChannelToResolve.future;
}