Merge "Update split screen UI to support light theme." into udc-dev am: 7f886bf4 am: 57fec030

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21617533



Change-Id: I7d6334548f52fa7c6296742cbf0a3caed4392560
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>