Reorganize Transport.Stdio files

This change reorganizes the files in the Transport.Stdio library to
prepare for a split in message structure between language server and debug
adapter messages.  The following commits will change class hierarchy and
namespaces for all affected files.

Author: daviwil

src/PowerShellEditorServices.Host/StdioConsoleHost.cs

@@ -43,28 +43,30 @@ Task<int> IConsoleHost.PromptForChoice(
             IEnumerable<ChoiceDetails> choices,
             int defaultChoice)
         {
-            // Create and store a TaskCompletionSource that will be
-            // used to send the user's response back to the caller
-            this.currentPromptChoiceTask = new TaskCompletionSource<int>();
-            this.currentReplEventSequence++;
-
-            this.messageWriter.WriteMessage(
-                new ReplPromptChoiceEvent
-                {
-                    Body = new ReplPromptChoiceEventBody
-                    {
-                        Seq = this.currentReplEventSequence,
-                        Caption = caption,
-                        Message = message,
-                        DefaultChoice = defaultChoice,
-                        Choices = 
-                            choices
-                                .Select(ReplPromptChoiceDetails.FromChoiceDescription)
-                                .ToArray()
-                    }
-                });
-
-            return this.currentPromptChoiceTask.Task;
+            //// Create and store a TaskCompletionSource that will be
+            //// used to send the user's response back to the caller
+            //this.currentPromptChoiceTask = new TaskCompletionSource<int>();
+            //this.currentReplEventSequence++;
+
+            //this.messageWriter.WriteMessage(
+            //    new ReplPromptChoiceEvent
+            //    {
+            //        Body = new ReplPromptChoiceEventBody
+            //        {
+            //            Seq = this.currentReplEventSequence,
+            //            Caption = caption,
+            //            Message = message,
+            //            DefaultChoice = defaultChoice,
+            //            Choices = 
+            //                choices
+            //                    .Select(ReplPromptChoiceDetails.FromChoiceDescription)
+            //                    .ToArray()
+            //        }
+            //    });
+
+            //return this.currentPromptChoiceTask.Task;
+
+            throw new NotImplementedException("This method is currently being refactored and is not available.");
         }
 
         void IConsoleHost.PromptForChoiceResult(