Launch initial split from taskbar in overview app menu

* Consolidated init calls in SplitSelectStateController
* Also add support to launch from taskbar all apps
* Add logic in SplitSelectStateController to know whether
or not we need to dismiss existing TaskView vs relying
on mSplitHiddenTaskView null check
* Default click handling for SplitShortcut is to start
split selection mode

Bug: 251747761
Test: Initiated split from smart actions, thumbnail app
icon, home, taskbar in overview, all apps. Saw it choose
the latest thumbnail

Change-Id: Ib4f64e619c97615af458a19a9c0efd86c92979d9