feat: enhance PopConfirm with async command support and improve binding. add more demo.

src/Ursa.Themes.Semi/Controls/PopConfirm.axaml

@@ -12,7 +12,7 @@
                         ContentTemplate="{TemplateBinding ContentTemplate}" />
                     <Popup
                         IsLightDismissEnabled="True"
-                        IsOpen="{TemplateBinding IsDropdownOpen, Mode=TwoWay}"
+                        IsOpen="{Binding IsDropdownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
                         OverlayInputPassThroughElement="{Binding #PART_ContentPresenter}"
                         Name="{x:Static u:PopConfirm.PART_Popup}"
                         Placement="{TemplateBinding Placement}" >

src/Ursa/Controls/PopConfirm/PopConfirm.cs

@@ -201,8 +201,11 @@ public class PopConfirm : ContentControl
     protected override bool RegisterContentPresenter(ContentPresenter presenter)
     {
         var result = base.RegisterContentPresenter(presenter);
-        _childChangeDisposable = presenter.GetPropertyChangedObservable(ContentPresenter.ChildProperty)
-                                          .Subscribe(OnChildChanged);
+        if (result)
+        {
+            _childChangeDisposable = presenter.GetPropertyChangedObservable(ContentPresenter.ChildProperty)
+                                              .Subscribe(OnChildChanged);
+        }
         return result;
     }