Define Heading levels in Settings App (#7496)

* Add shell page headings

* add headings for all the PTsettings

* add heading level 1 for the heading of each page

* Add heading level to the style instead of redifining it multiple times

* revert adding level2 for each control

* add heading level for run as admin because it does not follow the group style and rather the default style

src/core/Microsoft.PowerToys.Settings.UI/Styles/TextBlock.xaml

@@ -22,6 +22,7 @@
     <Style x:Key="SettingsGroupTitleStyle" TargetType="TextBlock" BasedOn="{StaticResource SubtitleTextBlockStyle}">
         <Setter Property="Margin" Value="0,34,0,4" />
         <Setter Property="FontWeight" Value="SemiBold"/>
+        <Setter Property="AutomationProperties.HeadingLevel" Value="Level2" />
     </Style>
 
     <Style x:Key="SettingsGroupTitleStyleAsHeader" TargetType="TextBlock" BasedOn="{StaticResource SettingsGroupTitleStyle}">