Composite Actions Support for Multiple Run Steps (#549)

* Composite Action Run Steps

* Clean up trace messages + add Trace debug in ActionManager

* Change String to string

* Add comma to Composite

* Change JobSteps to a List, Change Register Step function name

* Add TODO, remove unn. content

* Remove unnecessary code

* Fix unit tests

* Add verbose trace logs which are only viewable by devs

* Sort usings in Composite Action Handler

* Change 0 to location

* Update context variables in composite action yaml

* Add helpful error message for null steps

src/Runner.Worker/JobRunner.cs

@@ -152,7 +152,7 @@ namespace GitHub.Runner.Worker
                 {
                     foreach (var step in jobSteps)
                     {
-                        jobContext.JobSteps.Enqueue(step);
+                        jobContext.JobSteps.Add(step);
                     }
 
                     await stepsRunner.RunAsync(jobContext);