Merge "Update split screen UI to support light theme." into tm-qpr-dev am: 767ab1e8

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21592580



Change-Id: Ia4f5f97c44198fc9d78906a33a643b8fc4ed52f7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>