Merge "Add a system API UpdateEngine to switch the slot back and forth" am: 4eaa49eeb6 am: 7c7696cd47 am: 547296b419 am: ee4e466a09

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1698090

Change-Id: I20516865284f9c4c2fc24e5b28a40a38dcd1a9a0