Make sure to hide IME adjust dims when exiting split mode

If the IME is showing while exiting split mode, the IME-adjust dims
won't be changed to hidden. This makes sure to hide the IME-adjust dims
when leaving split mode. This phases in fix of ag/12683264 to R.

Bug: 168505685
Fix: 181781489
Test: atest WMShellUnitTests
Test: manual check switching user while showing IME in split mode,
      there won't have overlapping dim remains on the screen.
Merged-In: I778df71616827c01f415231d8bbc20b037181d10
Change-Id: Ib7b843effd6c58e2d2546c8845a629701d87a521