Freeze the configuration size when shifting split layout so that client
apps can calculate insets properly and won't get config or relaunch.
Fix: 192410210
Test: atest WMShellUnitTests
Test: verified the content of the bottom split won't be truncated when
adjusting split layout with IME and won't get relaunch.
Change-Id: I38da063ffacc19b691c14b74d118949293414492
da44526b9b