replace v6 with experimental v7 code

src/MpvNet.Windows/WPF/BindingProxy.cs

@@ -0,0 +1,20 @@
+
+using System.Windows;
+
+namespace MpvNet.Windows.WPF;
+
+public class BindingProxy : Freezable
+{
+    protected override Freezable CreateInstanceCore() => new BindingProxy();
+
+    public object Data
+    {
+        get { return GetValue(DataProperty); }
+        set { SetValue(DataProperty, value); }
+    }
+
+    // Using a DependencyProperty as the backing store for Data.
+    // This enables animation, styling, binding, etc...
+    public static readonly DependencyProperty DataProperty =
+        DependencyProperty.Register("Data", typeof(object), typeof(BindingProxy), new UIPropertyMetadata(null));
+}