Update Focus Visual to adapt to platform values if WinUI being used

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI.Controls/TokenizingTextBox/TokenizingTextBox.xaml

@@ -8,10 +8,10 @@
     </ResourceDictionary.MergedDictionaries>
 
     <!--  Resources for TokenizingTextBox  -->
-    <Thickness x:Key="TokenizingTextBoxBorderThickness">2</Thickness>
     <Thickness x:Key="TokenizingTextBoxPadding">4</Thickness>
     <Thickness x:Key="TokenizingTextBoxPresenterMargin">0,0,6,0</Thickness>
     <x:Double x:Key="TokenizingTextBoxTokenSpacing">2</x:Double>
+    <Thickness x:Key="TextControlBorderThemeThicknessFocused">2</Thickness>
 
     <controls:TokenizingTextBoxStyleSelector x:Key="TokenizingTextBoxStyleSelector"
                                              TextStyle="{StaticResource TokenizingTextBoxItemTextStyle}"
@@ -23,7 +23,7 @@
         <Setter Property="Foreground" Value="{ThemeResource TextControlForeground}" />
         <Setter Property="Background" Value="{ThemeResource TextControlBackground}" />
         <Setter Property="BorderBrush" Value="{ThemeResource TextControlBorderBrush}" />
-        <Setter Property="BorderThickness" Value="{StaticResource TokenizingTextBoxBorderThickness}" />
+        <Setter Property="BorderThickness" Value="{StaticResource TextControlBorderThemeThickness}" />
         <Setter Property="IsTabStop" Value="False" />
         <Setter Property="TabNavigation" Value="Once" />
         <Setter Property="IsSwipeEnabled" Value="False" />
@@ -135,6 +135,12 @@
 
                 <VisualStateGroup x:Name="FocusStates">
                     <VisualState x:Name="Focused">
+                        <Storyboard>
+                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="FocusVisual" Storyboard.TargetProperty="BorderThickness">
+                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource TextControlBorderThemeThicknessFocused}" />
+                            </ObjectAnimationUsingKeyFrames>
+                        </Storyboard>
+                        
                         <VisualState.Setters>
                             <Setter Target="FocusVisual.Opacity" Value="1" />
                         </VisualState.Setters>