Support split resizing while showing floating IME panel

Enable to rezise split screen while showing floating IME panel or
attached with physical keyboard in input mode.

Fix: 269071345
Test: atest WMShellUnitTests
Video: http://recall/-/fLARJNt42LVxc3tt86SneW/fITd3BUUAtmo91u22R3cd0
       http://recall/-/fLARJNt42LVxc3tt86SneW/eFnwHQNgvM7OautAX3N4rP
Change-Id: Ifc9ff0cefbcaaaef598c9ae0fee545bd8ddba486