feat: make button group functional. Update Demo.

demo/Ursa.Demo/Pages/ButtonGroupDemo.axaml

@@ -13,10 +13,20 @@
     mc:Ignorable="d">
 
     <StackPanel Margin="20" Spacing="20">
-        <u:ButtonGroup Classes="Primary Solid" ItemsSource="{Binding Items}" />
-        <u:ButtonGroup Classes="Primary" ItemsSource="{Binding Items}" />
-        <u:ButtonGroup Classes="Primary Borderless" ItemsSource="{Binding Items}" />
-        <u:ButtonGroup Classes="Primary Large" ItemsSource="{Binding Items}" />
-        <u:ButtonGroup Classes="Primary Small" ItemsSource="{Binding Items}" />
+        <u:ButtonGroup Classes="Primary Solid" 
+                       CommandBinding="{Binding InvokeCommand}"
+                       ItemsSource="{Binding Items}" >
+            <u:ButtonGroup.ItemTemplate>
+                <DataTemplate x:DataType="vm:ButtonItem">
+                    <TextBlock Text="{Binding Name}" Foreground="{DynamicResource SemiGrey3}"></TextBlock>
+                </DataTemplate>
+            </u:ButtonGroup.ItemTemplate>
+        </u:ButtonGroup>
+        
+        <u:ButtonGroup Classes="Primary" 
+                       ContentBinding="{Binding Name}"
+                       CommandBinding="{Binding InvokeCommand}"
+                       ItemsSource="{Binding Items}" >
+        </u:ButtonGroup>
     </StackPanel>
 </UserControl>

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);
+    }
 }