[OOBE] Refactor UI code, minor UI tweaks (#16578)

* Move content to dedicated XAML

* Select modules enum

* Remove redundant code, UI fixes

* Markdown rendering tweaks

* Address feedback

src/settings-ui/Settings.UI/OOBE/Enums/PowerToysModulesEnum.cs

@@ -7,7 +7,6 @@ namespace Microsoft.PowerToys.Settings.UI.OOBE.Enums
     public enum PowerToysModulesEnum
     {
         Overview = 0,
-        WhatsNew,
         AlwaysOnTop,
         Awake,
         ColorPicker,
@@ -20,5 +19,6 @@ namespace Microsoft.PowerToys.Settings.UI.OOBE.Enums
         Run,
         ShortcutGuide,
         VideoConference,
+        WhatsNew,
     }
 }