Moved Shortcut helper customization mode state management

The customization mode state management has been moved from the UI layer
to a repository to allow for multiple points of entry to customization
mode.

Fix: 403240110
Flag: com.android.systemui.extended_apps_shortcut_category
Test: ShortcutHelperViewModelTest,
ShortcutCustomizationModeRepositoryTest

Change-Id: I042a0d8a3731c73193304a6f3f40f476d40f05e0