fix: Clip ripple effect for default Button style in materialDesign:PopupBox (#3983)

* fix: Clip ripple effect for default Button style in `materialDesign:PopupBox`
Use the BorderClipConverter to clip the ripple to the bounds of the button

* refactor: leverage ClipToBounds instead of a custom converter
Set ClipToBounds="True" instead of using the `BorderClipConverter` in the Button ControlTemplate to prevent child elements from rendering outside the template boundaries.

Author: corvinsz

src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PopupBox.xaml

@@ -17,7 +17,7 @@
     <Setter Property="Template">
       <Setter.Value>
         <ControlTemplate TargetType="{x:Type Button}">
-          <Grid>
+          <Grid ClipToBounds="True">
             <VisualStateManager.VisualStateGroups>
               <VisualStateGroup Name="CommonStates">
                 <VisualStateGroup.Transitions>