Use global SystemParameters.FocusVisualStyleKey insead of per control FocusVisual style

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**Is your feature request related to a problem? Please describe.**
A [bunch](https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/search?q=FocusVisual) 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:
```xaml

<Setter Property="Control.Template">
...
</Setter>

```

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`:
```xaml

<Setter Property="materialDesign:FocusVisualAssist.Margin" Value="0,0,0,0"/>

```

Commencez par les définitions de FocusVisual dans MaterialDesignTheme.Button.xaml et MaterialDesignTheme.RadioButton.xaml, puis examinez l’utilisation proposée de SystemParameters.FocusVisualStyleKey dans App.xaml. Comparez le modèle partagé et la marge différente de OptionMark, et prenez en compte le chemin FocusVisualAssist existant. Le travail est considéré comme terminé lorsque les styles dupliqués par contrôle sont remplacés ou consolidés sans modifier le rendu du focus.

Rédigé par le modèle d'indexation à partir du texte de l'issue.