optimized demo start-up speed

src/Shared/HandyControlDemo_Shared/Resources/DemoTheme.cs

@@ -8,9 +8,12 @@ namespace HandyControlDemo.Resources
 {
     public class DemoTheme : Theme
     {
-        public override Uri ThemeUri => new Uri("pack://application:,,,/HandyControlDemo;component/Resources/Themes/Theme.xaml");
-
         public override ResourceDictionary GetSkin(SkinType skinType) =>
             ResourceHelper.GetSkin(typeof(App).Assembly, "Resources/Themes", skinType);
+
+        public override ResourceDictionary GetTheme() => new ResourceDictionary
+        {
+            Source = new Uri("pack://application:,,,/HandyControlDemo;component/Resources/Themes/Theme.xaml")
+        };
     }
 }