Adding get/put and compare-and-set methods to Unsafe am: 507cf90521 am: 4cb8cab577 am: d68684a2c1

Original change: https://android-review.googlesource.com/c/platform/art/+/1846390

Change-Id: I36767f2a1c1128058058cb8b4da0e27a2dda1dc9