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

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

Change-Id: I0a7c4f7fca1192cedbd006c03defb32783465646