Added repository to expose app shortcuts for user visible apps

This repository takes all user visible apps on the device for the
current user and creates a Shortcut category for these apps. This
shortcut category is supplied to Shortcut helper categories interactor
and flows downstream to shortcut helper to be displayed when in
customization mode;

Flag: com.android.systemui.extended_apps_shortcut_category
Test: AppsShortcutCategoryRepositoryTest,
ShortcuthelperCategoriesInteractorTest
Fix: 403243867

Change-Id: Ibac3af87671bf0aca2d40ee5d39f18986c91c595