Only give DisplayInsetsController control over IME in split-screen

There is additional jank risk as well as animation curves aren't
fully aligned with InsetsController, we should limit the scope
where we use that controller for now. Once we have better
alignment with InsetsController, we can expand it's usage again.

Test: DisplayContentTests
Test: Open IME in Bubbles
Bug: 152197007
Change-Id: Ic8e925842b28c08fc6ea9ba58c7c05627b5a4eaa