Display access key in RadioButton.

samples/ControlCatalog/Pages/RadioButtonPage.xaml

@@ -11,9 +11,9 @@
                 Spacing="16">
       <StackPanel Orientation="Vertical"
                   Spacing="16">
-        <RadioButton IsChecked="True">Option 1</RadioButton>
-        <RadioButton>Option 2</RadioButton>
-        <RadioButton IsChecked="{x:Null}">Option 3</RadioButton>
+        <RadioButton IsChecked="True">_Option 1</RadioButton>
+        <RadioButton>O_ption 2</RadioButton>
+        <RadioButton IsChecked="{x:Null}">Op_tion 3</RadioButton>
         <RadioButton IsEnabled="False">Disabled</RadioButton>
       </StackPanel>
       <StackPanel Orientation="Vertical"

src/Avalonia.Themes.Default/RadioButton.xaml

@@ -31,6 +31,7 @@
                             ContentTemplate="{TemplateBinding ContentTemplate}"
                             Content="{TemplateBinding Content}"
                             Margin="4,0,0,0"
+                            RecognizesAccessKey="True"
                             VerticalAlignment="Center"
                             Grid.Column="1"/>
         </Grid>

src/Avalonia.Themes.Fluent/Controls/RadioButton.xaml

@@ -51,6 +51,7 @@
                               ContentTemplate="{TemplateBinding ContentTemplate}"
                               TextBlock.Foreground="{TemplateBinding Foreground}"
                               Margin="{TemplateBinding Padding}"
+                              RecognizesAccessKey="True"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                               VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                               Grid.Column="1" />