feat: make button group functional. Update Demo.

demo/Ursa.Demo/ViewModels/ButtonGroupDemoViewModel.cs

@@ -1,11 +1,35 @@
 using System.Collections.ObjectModel;
+using System.Threading.Tasks;
+using System.Windows.Input;
+using CommunityToolkit.Mvvm.Input;
+using Ursa.Controls;
 
 namespace Ursa.Demo.ViewModels;
 
 public class ButtonGroupDemoViewModel: ViewModelBase
 {
-    public ObservableCollection<string> Items { get; set; } = new ()
+    public ObservableCollection<ButtonItem> Items { get; set; } = new ()
     {
-        "Ding", "Otter", "Husky", "Mr. 17", "Cass"
+        new ButtonItem(){Name = "Ding" },
+        new ButtonItem(){Name = "Otter" },
+        new ButtonItem(){Name = "Husky" },
+        new ButtonItem(){Name = "Mr. 17" },
+        new ButtonItem(){Name = "Cass" },
     };
+}
+
+public class ButtonItem
+{
+    public string? Name { get; set; }
+    public ICommand InvokeCommand { get; set; }
+
+    public ButtonItem()
+    {
+        InvokeCommand = new AsyncRelayCommand(Invoke);
+    }
+
+    private async Task Invoke()
+    {
+        await MessageBox.ShowAsync("Hello " + Name);
+    }
 }