This change involves:
> Migrating CarHeadsUpNotificationSystemContainer to extend instead of
implement the new implementation of CarHeadsUpNotificationContainer to
accomodate for prioritized HUNs.
> Migrating bottom HUNs resources to Notifications package.
Bug: 112155307
Test: Manual
Change-Id: I8fd2d8380d69174564b9899986e81c702b7018d1