the MaterialDesignUserForegroundCheckBox style for custom checkboxsize (#3743)

* RadioButton 添加自定义大小功能

* Adding sample to normal WPF demo app as well

* the MaterialDesignUserForegroundCheckBox style  for custom checkboxsize

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Co-authored-by: Kevin Bost <kitokeboo@gmail.com>

Author: mzy666888

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

@@ -239,8 +239,8 @@
               <ColumnDefinition Width="Auto" />
               <ColumnDefinition Width="*" />
             </Grid.ColumnDefinitions>
-            <Viewbox Width="18"
-                     Height="18"
+            <Viewbox Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:CheckBoxAssist.CheckBoxSize)}"
+                     Height="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:CheckBoxAssist.CheckBoxSize)}"
                      VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                      FlowDirection="LeftToRight">
               <Canvas Width="24" Height="24">