Transform Pocket Demo to be featured application example

Why
Pocket demo is nice looking but was initially created to be a demo. Therefore it's too large and doesn't follow example guidelines to be an example without modifications.

What

• Project should be runnable in both Qt Design Studio (qmlproject) and Qt Creator (CMake)
• The name should be changed to something more descriptive e.g. FX & Material Showroom
• Documentation should be added
• Make all the assets downloadable and add Loading screen that shows the progress
• Refactor the code to follow Qt6 example guidelines
• Move project to qtdoc repo

Project repo
https://git.qt.io/playground/pocket-demo