Update with next sass example (#73548)
This PR updates the `with-next-sass` 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
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Co-authored-by: Sam Ko <sam@vercel.com>
