Fix missing prompt when launching temporary interactive debug session

This change fixes an issue which causes the command prompt to not appear
when you start an interactive debugging session with the
-DebugServiceOnly parameter.  The fix is to invoke the host's command
loop in this specific case.

Resolves PowerShell/vscode-powershell#942

src/PowerShellEditorServices.Host/EditorServicesHost.cs

@@ -407,6 +407,7 @@ private EditorSession CreateDebugSession(
 
             editorSession.StartDebugSession(
                 powerShellContext,
+                hostUserInterface,
                 editorOperations);
 
             return editorSession;

src/PowerShellEditorServices.Protocol/Server/DebugAdapter.cs

@@ -217,14 +217,23 @@ protected async Task HandleConfigurationDoneRequest(
 
             await requestContext.SendResult(null);
 
-            if (this.isInteractiveDebugSession &&
-                this.editorSession.DebugService.IsDebuggerStopped)
+            if (this.isInteractiveDebugSession)
             {
-                // If this is an interactive session and there's a pending breakpoint,
-                // send that information along to the debugger client
-                this.DebugService_DebuggerStopped(
-                    this,
-                    this.editorSession.DebugService.CurrentDebuggerStoppedEventArgs);
+                if (this.ownsEditorSession)
+                {
+                    // If this is a debug-only session, we need to start
+                    // the command loop manually
+                    this.editorSession.HostInput.StartCommandLoop();
+                }
+
+                if (this.editorSession.DebugService.IsDebuggerStopped)
+                {
+                    // If this is an interactive session and there's a pending breakpoint,
+                    // send that information along to the debugger client
+                    this.DebugService_DebuggerStopped(
+                        this,
+                        this.editorSession.DebugService.CurrentDebuggerStoppedEventArgs);
+                }
             }
         }
 
@@ -646,7 +655,7 @@ protected async Task HandleStackTraceRequest(
             int startFrameIndex = stackTraceParams.StartFrame ?? 0;
             int maxFrameCount = stackFrames.Length;
 
-            // If the number of requested levels == 0 (or null), that means get all stack frames 
+            // If the number of requested levels == 0 (or null), that means get all stack frames
             // after the specified startFrame index. Otherwise get all the stack frames.
             int requestedFrameCount = (stackTraceParams.Levels ?? 0);
             if (requestedFrameCount > 0)

src/PowerShellEditorServices/Session/EditorSession.cs

@@ -123,14 +123,17 @@ public void StartSession(
         /// for the ConsoleService.
         /// </summary>
         /// <param name="powerShellContext"></param>
+        /// <param name="hostInput"></param>
         /// <param name="editorOperations">
         /// An IEditorOperations implementation used to interact with the editor.
         /// </param>
         public void StartDebugSession(
             PowerShellContext powerShellContext,
+            IHostInput hostInput,
             IEditorOperations editorOperations)
         {
             this.PowerShellContext = powerShellContext;
+            this.HostInput = hostInput;
 
             // Initialize all services
             this.RemoteFileManager = new RemoteFileManager(this.PowerShellContext, editorOperations, logger);