feat: fix oversize dialog.

demo/Ursa.Demo/Dialogs/PlainDialog.axaml

@@ -9,5 +9,6 @@
              x:Class="Ursa.Demo.Dialogs.PlainDialog">
     <StackPanel>
         <Calendar SelectedDate="{Binding Date}" ></Calendar>
+        <TextBlock TextWrapping="Wrap" Text="{Binding Text}"></TextBlock>
     </StackPanel>
 </UserControl>

demo/Ursa.Demo/Dialogs/PlainDialogViewModel.cs

@@ -12,4 +12,17 @@ public class PlainDialogViewModel: ObservableObject
         get => _date;
         set => SetProperty(ref _date, value);
     }
+
+    private string? _text;
+    public string? Text
+    {
+        get => _text;
+        set => SetProperty(ref _text, value);
+    }
+
+    public PlainDialogViewModel()
+    {
+        Text =
+            "千古悠悠 有多少冤魂嗟叹 空怅望人寰无限 丛生哀怨 泣血蝇虫笑苍天 孤帆叠影锁白链 残月升骤起烈烈风 尽吹散 尽吹散 尽吹散 滂沱雨无底涧 涉激流登彼岸 奋力拨云间消得雾患 社稷安抚臣子心 长驱鬼魅不休战 看斜阳照大地阡陌 从头转";
+    }
 }