Fix debugger startup hang when session still initializing

This change fixes a hang that occurs when the user starts the debugger
right when the PowerShell session is still initializing.  This is caused
by a call to PowerShellContext.SetWorkingDirectory which isn't
respecting the current state of the runspace.  The fix is to ask for a
RunspaceHandle to ensure that the runspace is free before attempting to
set the working directory.

Resolves PowerShell/vscode-powershell#632

Author: daviwil

src/PowerShellEditorServices.Protocol/Server/DebugAdapter.cs

@@ -200,7 +200,7 @@ protected override void Shutdown()
                 this.editorSession = null;
             }
         }
-
+        
         #region Built-in Message Handlers
 
         protected async Task HandleConfigurationDoneRequest(
@@ -273,7 +273,7 @@ protected async Task HandleLaunchRequest(
             // TODO: What's the right approach here?
             if (this.editorSession.PowerShellContext.CurrentRunspace.Location == RunspaceLocation.Local)
             {
-                editorSession.PowerShellContext.SetWorkingDirectory(workingDir);
+                await editorSession.PowerShellContext.SetWorkingDirectory(workingDir);
                 Logger.Write(LogLevel.Verbose, "Working dir set to: " + workingDir);
             }
 

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -183,7 +183,7 @@ protected async Task HandleInitializeRequest(
             // Set the working directory of the PowerShell session to the workspace path
             if (editorSession.Workspace.WorkspacePath != null)
             {
-                editorSession.PowerShellContext.SetWorkingDirectory(
+                await editorSession.PowerShellContext.SetWorkingDirectory(
                     editorSession.Workspace.WorkspacePath);
             }
 

src/PowerShellEditorServices/Session/PowerShellContext.cs

@@ -1048,9 +1048,12 @@ internal void ReleaseRunspaceHandle(RunspaceHandle runspaceHandle)
         /// unescaped before calling this method.
         /// </summary>
         /// <param name="path"></param>
-        public void SetWorkingDirectory(string path)
+        public async Task SetWorkingDirectory(string path)
         {
-            this.CurrentRunspace.Runspace.SessionStateProxy.Path.SetLocation(path);
+            using (RunspaceHandle runspaceHandle = await this.GetRunspaceHandle())
+            {
+                runspaceHandle.Runspace.SessionStateProxy.Path.SetLocation(path);
+            }
         }
 
         /// <summary>