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.

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