[5.0] Derive name of app folder from output of app_path() vs hard-coding "app/"

Recently added was the new AppNamespaceDetectorTrait in Illuminate\Console. In it, it attempts to figure out the base namespace for the application by inspecting the PSR-4 autoload section of the composer.json. It currently is hard-coded to looking for a namespace mapped to "app/". However, since this folder can be changed via settings in bootstrap/paths.php, it shouldn't assume the name of the app folder.

For instance, I like to have an app_server folder for my Laravel application and an app_client folder for my Angular application. I then have a gulp task that compiles my Angular application and publishes it in the public/js folder
`$appFolderName` should be used rather than `$app_folder_name` please.