feat: initialize, setup demo. make sure MVVM works.

demo/Ursa.Demo/ViewModels/ToolBarDemoViewModel.cs

@@ -0,0 +1,72 @@
+using System.Collections.ObjectModel;
+using System.Windows.Input;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Ursa.Controls;
+
+namespace Ursa.Demo.ViewModels;
+
+public partial class ToolBarDemoViewModel: ObservableObject
+{
+    public ObservableCollection<ToolBarItemViewModel> Items { get; set; }
+    public ToolBarDemoViewModel()
+    {
+        Items = new()
+        {
+            new ToolBarButtonItemViewModel() { Content = "New" },
+            new ToolBarButtonItemViewModel() { Content = "Open" },
+            new ToolBarButtonItemViewModel() { Content = "Save" },
+            new ToolBarCheckBoxItemViweModel() { Content = "Bold" },
+            new ToolBarCheckBoxItemViweModel() { Content = "Italic" },
+            new ToolBarComboBoxItemViewModel() { Content = "Font Size", Items = new (){ "10", "12", "14"  } }
+        };
+    }
+}
+
+public abstract class ToolBarItemViewModel: ObservableObject
+{
+    
+}
+
+public class ToolBarButtonItemViewModel: ToolBarItemViewModel
+{
+    public string Content { get; set; }
+    public ICommand Command { get; set; }
+
+    public ToolBarButtonItemViewModel()
+    {
+        Command = new AsyncRelayCommand(async () => { await MessageBox.ShowOverlayAsync(Content); });
+    }
+}
+
+public class ToolBarCheckBoxItemViweModel: ToolBarItemViewModel
+{
+    public string Content { get; set; }
+    public bool IsChecked { get; set; }
+    public ICommand Command { get; set; }
+
+    public ToolBarCheckBoxItemViweModel()
+    {
+        Command = new AsyncRelayCommand(async () => { await MessageBox.ShowOverlayAsync(Content); });
+    }
+}
+
+public class ToolBarComboBoxItemViewModel: ToolBarItemViewModel
+{
+    public string Content { get; set; }
+    public ObservableCollection<string> Items { get; set; }
+
+    private string _selectedItem;
+    public string SelectedItem
+    {
+        get => _selectedItem;
+        set
+        {
+            SetProperty(ref _selectedItem, value);
+            MessageBox.ShowOverlayAsync(value);
+        }
+    }
+    
+    
+    
+}