ListDetailsView: unfocuse all children in details on selection changed

Author: Rosuavio

Microsoft.Toolkit.Uwp.UI.Controls.Layout/ListDetailsView/ListDetailsView.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections.Generic;
+using System.Linq;
 using Windows.ApplicationModel;
 using Windows.UI.Core;
 using Windows.UI.Xaml;
@@ -292,6 +293,11 @@ private void SetDetailsContent()
         {
             if (_detailsPresenter != null)
             {
+                foreach(var child in _detailsPresenter.FindChildren().OfType<Control>())
+                {
+                    child.Focus(FocusState.Unfocused);
+                }
+
                 // Update the content template:
                 if (_detailsPresenter.ContentTemplateSelector != null)
                 {