Merge "Finish supporting floating-IME alpha in split-screen" into rvc-dev am: 9c9434b30f am: b1e36dba36 am: 2031024be7 am: ad2094ef33

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12130198

Change-Id: Iebeb6e3a4e5de022c8b21374f9076c3a2e5653e6