chore: rename demo class names.

src/Shared/HandyControlDemo_Shared/UserControl/Controls/PreviewSliderDemo.xaml.cs

@@ -1,9 +1,9 @@
 
 namespace HandyControlDemo.UserControl;
 
-public partial class PreviewSliderDemoCtl
+public partial class PreviewSliderDemo
 {
-    public PreviewSliderDemoCtl()
+    public PreviewSliderDemo()
     {
         InitializeComponent();
     }