Merge "Finish supporting floating-IME alpha in split-screen" into rvc-dev am: 9c9434b30f am: 54545eb6c3

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

Change-Id: I5aa5075279136f6921eb37991764e598a1153ed6