feat: add overlay dialog sample.

demo/Ursa.Demo/Dialogs/DialogWithActionViewModel.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Windows.Input;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Ursa.Controls;
+
+namespace Ursa.Demo.Dialogs;
+
+public partial class DialogWithActionViewModel: ObservableObject, IDialogContext
+{
+    [ObservableProperty] private string _title;
+    [ObservableProperty] private DateTime _date;
+    public object? DefaultCloseResult { get; set; } = true;
+    public event EventHandler<object>? Closed;
+    
+    public ICommand OKCommand { get; set; }
+    public ICommand CancelCommand { get; set; }
+    
+    public DialogWithActionViewModel()
+    {
+        OKCommand = new RelayCommand(OK);
+        CancelCommand = new RelayCommand(Cancel);
+        Title = "Please select a date";
+        Date = DateTime.Now;
+    }
+
+    private void OK()
+    {
+        Closed?.Invoke(this, true);
+    }
+
+    private void Cancel()
+    {
+        Closed?.Invoke(this, false);
+    }
+}