Restore split layout when wm-shell no longer controlling IME

Add a callback in ImePositionProcessor to notify IME cotnrol target
changed. And make sure to restore the split layout when wm-shell is not
contorlling IME insets anymore.

Fix: 174119991
Test: 1. open IME on the bootom split to adjust split layout with IME
      2. focus on direct reply of open passwork keyguard
      3. observe the split layout been restored after back to split

Change-Id: I5caeeff9406d21e21c8a82c0078cbfae36bd4063
Merged-In: I5caeeff9406d21e21c8a82c0078cbfae36bd4063