Allow system to disable behavior of pausing animators for bg apps am:...

Allow system to disable behavior of pausing animators for bg apps am: 161732cf am: 339361ad am: 7e79d7c1

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/18527682



Change-Id: I52c399fc1954bfac5f38ec0a5eca4c6008f220c5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>