[Gallery] Move searchbox and menu button to titlebar

<img width="1025" alt="image" src="https://github.com/CommunityToolkit/Tooling-Windows-Submodule/assets/9866362/97d51b86-24b8-419c-8af0-65d7fce6c9ee">

Per design guidelines, we should move the searchbox and menu button to the titlebar. This will give us some (much needed) vertical space back as well since we have a lot of menu items to show.