feat: add new dialog samples.

demo/Ursa.Demo/Dialogs/DefaultDemoDialogViewModel.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using Irihi.Avalonia.Shared.Contracts;
+
+namespace Ursa.Demo.Dialogs;
+
+public partial class DefaultDemoDialogViewModel: ObservableObject, IDialogContext
+{
+    public ObservableCollection<string> Cities { get; set; }
+    [ObservableProperty] private string? _owner;
+    [ObservableProperty] private string? _department;
+    [ObservableProperty] private string? _target;
+    [ObservableProperty] private string? _city;
+
+    public DefaultDemoDialogViewModel()
+    {
+        Cities =
+        [
+            "Shanghai", "Beijing", "Hulunbuir", "Shenzhen", "Hangzhou", "Nanjing", "Chengdu", "Wuhan", "Chongqing",
+            "Suzhou", "Tianjin", "Xi'an", "Qingdao", "Dalian"
+        ];
+    }
+    
+    public void Close()
+    {
+        RequestClose?.Invoke(this, null);
+    }
+
+    public event EventHandler<object?>? RequestClose;
+}