enhance: show the Submodule Change Details window on the same screen of it's parent (sourcegit-scm#2264)

Signed-off-by: leo <longshuang@msn.cn>

Author: love-linger

src/Views/DiffView.axaml.cs

@@ -45,15 +45,10 @@ private void OnGotoLastChange(object _, RoutedEventArgs e)
 
         private void OnOpenSubmoduleRevisionCompare(object sender, RoutedEventArgs e)
         {
-            var owner = TopLevel.GetTopLevel(this) as Window;
-            if (owner == null)
-                return;
-
             if (sender is Button { DataContext: Models.SubmoduleDiff diff } && diff.CanOpenDetails)
             {
                 var vm = new ViewModels.SubmoduleRevisionCompare(diff);
-                var dailog = new SubmoduleRevisionCompare() { DataContext = vm };
-                dailog.Show(owner);
+                App.ShowWindow(vm);
             }
         }
     }