Add chapter 10 sample project

Chapter10/TemplateStudioSampleApp/Helpers/NavigationHelper.cs

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+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+namespace TemplateStudioSampleApp.Helpers;
+
+// Helper class to set the navigation target for a NavigationViewItem.
+//
+// Usage in XAML:
+// <NavigationViewItem x:Uid="Shell_Main" Icon="Document" helpers:NavigationHelper.NavigateTo="AppName.ViewModels.MainViewModel" />
+//
+// Usage in code:
+// NavigationHelper.SetNavigateTo(navigationViewItem, typeof(MainViewModel).FullName);
+public class NavigationHelper
+{
+    public static string GetNavigateTo(NavigationViewItem item) => (string)item.GetValue(NavigateToProperty);
+
+    public static void SetNavigateTo(NavigationViewItem item, string value) => item.SetValue(NavigateToProperty, value);
+
+    public static readonly DependencyProperty NavigateToProperty =
+        DependencyProperty.RegisterAttached("NavigateTo", typeof(string), typeof(NavigationHelper), new PropertyMetadata(null));
+}