enhance: optimized TreeView style

src/Shared/HandyControl_Shared/Themes/Styles/Base/ToggleBlockBaseStyle.xaml

@@ -5,6 +5,7 @@
     <Style x:Key="ToggleBlockBaseStyle" TargetType="hc:ToggleBlock">
         <Setter Property="VerticalContentAlignment" Value="Center"/>
         <Setter Property="HorizontalContentAlignment" Value="Center"/>
+        <Setter Property="Focusable" Value="False"/>
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="hc:ToggleBlock">
@@ -37,4 +38,4 @@
         </Setter>
     </Style>
 
-</ResourceDictionary>
+</ResourceDictionary>