Merge "Allow SystemBar configuration via XML." into rvc-qpr-dev am: 4dbcd829fb am: 36b52feeb7

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12181454

Change-Id: I6ef84cef8f71763baba5f130f16c36b4aaf427a6