chore: separated System.Windows.Interactivity code

src/Shared/System.Windows.Interactivity/IAttachedObject.cs

@@ -0,0 +1,11 @@
+using System.Windows;
+
+namespace HandyControl.Interactivity;
+
+public interface IAttachedObject
+{
+    void Attach(DependencyObject dependencyObject);
+    void Detach();
+
+    DependencyObject AssociatedObject { get; }
+}