Set StateManager to BackgroundAppState if end gesture is NEW_TASK

* QUICK_SWITCH_FROM_HOME was incorrectly used as that LauncherState
is only meant for quickswitching for the most recent task from
workspace

Bug: 265734073
Test: Tested quickswitch with fullscreen and splitscreen tasks
Change-Id: Ia81152927f57203cf6adb90254675bcf82a2e836