Add accessible name to C# code copy button in ControlExample (#786)

The C# 'Source code' copy button had no AutomationProperties.Name, so its UI Automation Name was derived from the Segoe icon glyph (U+E8C8), which lies in the Unicode Private Use Area (U+E000-U+F8FF). Screen readers and Accessibility Insights flagged this (MAS 4.1.2). Added AutomationProperties.Name=Copy C# Code and a matching tooltip, mirroring the sibling XAML copy button.

Fixes AzDO DevDiv#3018313

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mmanolova-msft

Sample Applications/WPFGallery/Controls/ControlExample.xaml

@@ -123,7 +123,7 @@
                                             Foreground="{DynamicResource TextFillColorPrimaryBrush}"
                                             Text="C#" />
 
-                                        <Button Grid.Column="1" Padding="8" Command="ApplicationCommands.Copy" CommandParameter="Copy_CSharpCode" FocusManager.IsFocusScope="True" >
+                                        <Button Grid.Column="1" Padding="8" Command="ApplicationCommands.Copy" CommandParameter="Copy_CSharpCode" FocusManager.IsFocusScope="True" ToolTipService.ToolTip="Copy to clipboard" AutomationProperties.Name="Copy C# Code" >
                                             <TextBlock FontFamily="{StaticResource SymbolThemeFontFamily}" Text="&#xE8C8;" />
                                         </Button>
                                     </Grid>