Add a keyboard shortcut for desktop to split.

Similar to fullscreen to split, ctrl + action + L/R should bring the
focused freeform window to split side stage.

Test: atest DesktopTasksController
Test: Manually trigger the shortcut to move it to split
Bug: 326062194
Flag: ACONFIG com.android.window.flags.enable_desktop_windowing_mode DEVELOPMENT
Change-Id: I459fc2fa00b821c279fa77e3616001e44dd32d58

Change-Id: I25a31a1ab49951a313f62184208ebdf6613ac557