Fixes TreeViewItem chevron arrow orientation in RightToLeft flow direction mode (#10744)

Co-authored-by: Dipesh Kumar <[email protected]>

Author: dipeshmsft

src/Microsoft.DotNet.Wpf/src/Themes/PresentationFramework.Fluent/Styles/TreeViewItem.xaml

@@ -14,6 +14,7 @@
     <system:Double x:Key="TreeViewItemChevronSize">10</system:Double>
     <system:Double x:Key="TreeViewItemFontSize">14</system:Double>
     <system:String x:Key="TreeViewChevronRightGlyph">&#xE76C;</system:String>
+    <system:String x:Key="TreeViewChevronLeftGlyph">&#xE76B;</system:String>
 
     <Style x:Key="ExpandCollapseToggleButtonStyle" TargetType="{x:Type ToggleButton}">
         <!--  Universal WPF UI focus  -->
@@ -43,6 +44,9 @@
                             Text="{StaticResource TreeViewChevronRightGlyph}" />
                     </Grid>
                     <ControlTemplate.Triggers>
+                        <Trigger Property="FlowDirection" Value="RightToLeft">
+                            <Setter TargetName="ChevronIcon" Property="Text" Value="{StaticResource TreeViewChevronLeftGlyph}" />
+                        </Trigger>
                         <Trigger Property="IsChecked" Value="True">
                             <Trigger.EnterActions>
                                 <BeginStoryboard>

src/Microsoft.DotNet.Wpf/src/Themes/PresentationFramework.Fluent/Themes/Fluent.Dark.xaml

@@ -5230,6 +5230,7 @@
   <system:Double x:Key="TreeViewItemChevronSize">10</system:Double>
   <system:Double x:Key="TreeViewItemFontSize">14</system:Double>
   <system:String x:Key="TreeViewChevronRightGlyph"></system:String>
+  <system:String x:Key="TreeViewChevronLeftGlyph"></system:String>
   <Style x:Key="ExpandCollapseToggleButtonStyle" TargetType="{x:Type ToggleButton}">
     <!--  Universal WPF UI focus  -->
     <Setter Property="FocusVisualStyle" Value="{DynamicResource DefaultCollectionFocusVisualStyle}" />
@@ -5247,6 +5248,9 @@
             <TextBlock x:Name="ChevronIcon" VerticalAlignment="Center" FontSize="{StaticResource TreeViewItemChevronSize}" FontFamily="{DynamicResource SymbolThemeFontFamily}" HorizontalAlignment="Center" Text="{StaticResource TreeViewChevronRightGlyph}" />
           </Grid>
           <ControlTemplate.Triggers>
+            <Trigger Property="FlowDirection" Value="RightToLeft">
+              <Setter TargetName="ChevronIcon" Property="Text" Value="{StaticResource TreeViewChevronLeftGlyph}" />
+            </Trigger>
             <Trigger Property="IsChecked" Value="True">
               <Trigger.EnterActions>
                 <BeginStoryboard>

src/Microsoft.DotNet.Wpf/src/Themes/PresentationFramework.Fluent/Themes/Fluent.HC.xaml

@@ -5170,6 +5170,7 @@
   <system:Double x:Key="TreeViewItemChevronSize">10</system:Double>
   <system:Double x:Key="TreeViewItemFontSize">14</system:Double>
   <system:String x:Key="TreeViewChevronRightGlyph"></system:String>
+  <system:String x:Key="TreeViewChevronLeftGlyph"></system:String>
   <Style x:Key="ExpandCollapseToggleButtonStyle" TargetType="{x:Type ToggleButton}">
     <!--  Universal WPF UI focus  -->
     <Setter Property="FocusVisualStyle" Value="{DynamicResource DefaultCollectionFocusVisualStyle}" />
@@ -5187,6 +5188,9 @@
             <TextBlock x:Name="ChevronIcon" VerticalAlignment="Center" FontSize="{StaticResource TreeViewItemChevronSize}" FontFamily="{DynamicResource SymbolThemeFontFamily}" HorizontalAlignment="Center" Text="{StaticResource TreeViewChevronRightGlyph}" />
           </Grid>
           <ControlTemplate.Triggers>
+            <Trigger Property="FlowDirection" Value="RightToLeft">
+              <Setter TargetName="ChevronIcon" Property="Text" Value="{StaticResource TreeViewChevronLeftGlyph}" />
+            </Trigger>
             <Trigger Property="IsChecked" Value="True">
               <Trigger.EnterActions>
                 <BeginStoryboard>

src/Microsoft.DotNet.Wpf/src/Themes/PresentationFramework.Fluent/Themes/Fluent.Light.xaml

@@ -5239,6 +5239,7 @@
   <system:Double x:Key="TreeViewItemChevronSize">10</system:Double>
   <system:Double x:Key="TreeViewItemFontSize">14</system:Double>
   <system:String x:Key="TreeViewChevronRightGlyph"></system:String>
+  <system:String x:Key="TreeViewChevronLeftGlyph"></system:String>
   <Style x:Key="ExpandCollapseToggleButtonStyle" TargetType="{x:Type ToggleButton}">
     <!--  Universal WPF UI focus  -->
     <Setter Property="FocusVisualStyle" Value="{DynamicResource DefaultCollectionFocusVisualStyle}" />
@@ -5256,6 +5257,9 @@
             <TextBlock x:Name="ChevronIcon" VerticalAlignment="Center" FontSize="{StaticResource TreeViewItemChevronSize}" FontFamily="{DynamicResource SymbolThemeFontFamily}" HorizontalAlignment="Center" Text="{StaticResource TreeViewChevronRightGlyph}" />
           </Grid>
           <ControlTemplate.Triggers>
+            <Trigger Property="FlowDirection" Value="RightToLeft">
+              <Setter TargetName="ChevronIcon" Property="Text" Value="{StaticResource TreeViewChevronLeftGlyph}" />
+            </Trigger>
             <Trigger Property="IsChecked" Value="True">
               <Trigger.EnterActions>
                 <BeginStoryboard>