Merge "Use CarUserManager and fix broken "add user" button" into rvc-qpr-dev am: 9d96ed4893 am: 13e1b6c7ff

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12181458

Change-Id: Ie94d1e53f6a041c9fd901282af3910fe663d2ff3