Correctly skip next prompt when interrupting foreground task

I believe this was the original intention, and indeed, debugging
shows that it is the correct behavior. On F8 we need to skip the
next prompt so the evaluated task runs instead, and then the
REPL correctly prompts after the evaluation is finished.

Author: andyleejordan

src/PowerShellEditorServices/Services/PowerShell/Host/PsesInternalHost.cs

@@ -270,11 +270,13 @@ public Task<T> InvokeTaskOnPipelineThreadAsync<T>(
                 //  - block the consumer thread from mutating the queue
                 //  - cancel any running task on the consumer thread
                 //  - place our task on the front of the queue
+                //  - skip the next prompt so the task runs instead
                 //  - unblock the consumer thread
                 using (_taskQueue.BlockConsumers())
                 {
                     CancelCurrentTask();
                     _taskQueue.Prepend(task);
+                    _skipNextPrompt = true;
                 }
 
                 return task.Task;