Merge "[Unfold transition] Fully manage the vignette on the background thread" into tm-qpr-dev am: c514109b3b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20725066

Change-Id: I6d7376119f00699a87b39f8be06995b03eeb2446
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>