Use global SystemParameters.FocusVisualStyleKey insead of per control FocusVisual style

Is your feature request related to a problem? Please describe.
A bunch of control styles define a FocusVisual style that is used as a setter value for FocusVisualStyle property and there is no way to customize them other than creating custom styles for each control and setting FocusVisualStyle to your own style.

Most of them are identical:
https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/blob/2a38b2c70a5e851bc5b926e0641c1848e719d86b/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.Button.xaml#L17-L30

Only OptionMarkFocusVisual seems to have different Margin:
https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/blob/2a38b2c70a5e851bc5b926e0641c1848e719d86b/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.RadioButton.xaml#L13-L25

I think the FocusVisualStyle should be globally defined with SystemParameters.FocusVisualStyleKey in App.xaml:

<Style x:Key="{x:Static SystemParameters.FocusVisualStyleKey}" TargetType="Control">
    <Setter Property="Control.Template"> 
        ...
    </Setter>
</Style>

If Margin is all that needs to be changed for some controls then maybe a FocusVisualAssist.Margin could be added to allow those controls to have their own FocusVisualStyle:

<Style x:Key="OptionMarkFocusVisual" BasedOn="{x:Static SystemParameters.FocusVisualStyleKey}">
    <Setter Property="materialDesign:FocusVisualAssist.Margin" Value="0,0,0,0"/>
</Style>

先从 MaterialDesignTheme.Button.xaml 和 MaterialDesignTheme.RadioButton.xaml 中的 FocusVisual 定义开始，然后检查 App.xaml 中对 SystemParameters.FocusVisualStyleKey 的拟议使用方式。比较共享模板和不同的 OptionMark 边距，并考虑现有的 FocusVisualAssist 路径。在不改变焦点呈现的情况下替换或合并按控件重复的样式，即表示完成。