Fix transition when leaving a split pair by home key

Pressing home key while in 3-button nav mode won't have an explicit
remote transition and thus need to lean on RemoteTransitionHandler to
fetch the proper remote transition from registered.
This makes sure to cover the flow for split screen so split screen
components won't need to deal with the recent transition by itself.

Fix: 273685456
Test: atest WMShellUnitTests WMShellFlickerTests
Test: http://recall/-/fLARJNt42LVxc3tt86SneW/c2pLS6FwyEMweiLiWqqzPa
Change-Id: Icf2739600601bb591dd865ba785151234de4fbd0