feat: add avalonia PathIcon style.

src/Avalonia/HandyControl_Avalonia/Themes/Styles/UserControl.axaml

@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
     <ControlTheme x:Key="{x:Type UserControl}"
                   TargetType="UserControl">
         <Setter Property="Template">