themed scroll bars, rounded courners, libmpv update

src/WPF/HandyControl/Controls/Attach/ScrollViewerAttach.cs

@@ -0,0 +1,18 @@
+
+using System.Windows;
+using HandyControl.Data;
+
+namespace HandyControl.Controls
+{
+    public class ScrollViewerAttach
+    {
+        public static readonly DependencyProperty AutoHideProperty = DependencyProperty.RegisterAttached(
+            "AutoHide", typeof(bool), typeof(ScrollViewerAttach), new FrameworkPropertyMetadata(ValueBoxes.TrueBox, FrameworkPropertyMetadataOptions.Inherits));
+
+        public static void SetAutoHide(DependencyObject element, bool value)
+            => element.SetValue(AutoHideProperty, value);
+
+        public static bool GetAutoHide(DependencyObject element)
+            => (bool) element.GetValue(AutoHideProperty);
+    }
+}