Show different message when PR not checked out

Let the user know they need to check out PR branch before navigating to editor.

Author: jcansdale

src/GitHub.App/Services/PullRequestEditorService.cs

@@ -469,8 +469,10 @@ void EnableNavigateToEditor(ITextView textView, IPullRequestSession session, IPu
             var view = vsEditorAdaptersFactory.GetViewAdapter(textView);
             EnableNavigateToEditor(view, session, file);
 
+            var statusMessage = session.IsCheckedOut ?
+                UI.Resources.NavigateToEditorStatusMessage : UI.Resources.NavigateToEditorNotCheckedOutStatusMessage;
             textView.GotAggregateFocus += (s, e) =>
-                statusBar.ShowMessage(VisualStudio.UI.Resources.NavigateToEditorStatusMessage);
+                StatusBarNotificationService.ShowMessage(statusMessage);
 
             textView.LostAggregateFocus += (s, e) =>
                 statusBar.ShowMessage(string.Empty);

src/GitHub.VisualStudio.UI/Resources.Designer.cs

@@ -419,4 +419,7 @@
   <data name="NavigateToEditorStatusMessage" xml:space="preserve">
     <value>Press Enter to navigate to Editor</value>
   </data>
+  <data name="NavigateToEditorNotCheckedOutStatusMessage" xml:space="preserve">
+    <value>Checkout PR branch and press Enter to navigate to Editor</value>
+  </data>
 </root>