Support workflow variables

[gurmitteotia]

It will be quite useful if user can store workflow specific state in variable. At the moment user will use either database or probably marker workflow action.

Here is how user can create workflow specific variables:

[WorkflowDescription("1.0")
public class OrderWorkflow : Workflow
{
  //Initialization is not needed
   private Variable<bool> _state1 = new Variable<bool>();
   private Variable<string> _state2 = new Variable<string>();
   private Variable<CustomObject> _state3 = new Variable<CustomObject>();
   [WorkflowVariable]
   private int _id =0;   

  //You can access these variables when workflow is executed
  [WorkflowEvent(EventName.Signal)]
  public WorkflowAction OnSignal(string signalName)
  {
     if(signalName == "set")
     {
            _state= true;
     }
     if (signalName  == "get")
    {
        if(_state.Value)
          return CompleteWorkflow("done");
    }
   return Ignore;
  }
}

Implementation note:

• Should store the variables in execution state.
• Lazy load the variables, when the first variable is accessed by calling DescribeWorkflowExecution API. This will avoid penalising the users who do not want to user variables.
• Total deserialized JSON length of variables should not exceed the length of 32768.