Add automation heading level 1 to fix about dialog (#15200)

Add automation heading level 1 to fix the about dialog by adding an
automation property.

Allows screen reader to pick up that this is a heading and read
properly.

Closes #11912

---------

Co-authored-by: Mike Griese <migrie@microsoft.com>

src/cascadia/TerminalApp/AboutDialog.xaml

@@ -17,7 +17,8 @@
 
     <StackPanel Orientation="Vertical">
         <TextBlock IsTextSelectionEnabled="True">
-            <Run Text="{x:Bind ApplicationDisplayName}" /> <LineBreak />
+            <Run AutomationProperties.HeadingLevel="1"
+                 Text="{x:Bind ApplicationDisplayName}" /> <LineBreak />
             <Run x:Uid="AboutDialog_VersionLabel" />
             <Run Text="{x:Bind ApplicationVersion}" />
         </TextBlock>