updated with-cssed example to utilize the app router. (#73348)
This PR updates the with-cssed example for using the App Router.
Here are the changes that have been made:
- I renamed the `pages` folder and moved it to the `app` folder.
- Added the layout.tsx file as part of the App Router.
- Updated the package.json file.
CC: @samcx
---------
Co-authored-by: Sam Ko <sam@vercel.com>
