Merge "Promote #setAdjacentTaskFragment to TestApi" into sc-v2-dev am: 2c452240ea am: 2e4d90b82c

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15528180

Change-Id: I37e3952c05a403d70db07dfc8dd633c4a34b4ddc