Allow single root candidate for app pair launch for pip edge case

* Shell will launch single task if requested split apps have one of them
already in Pip
* Create a separate method to set animation for launching from the
appPair icon on workspace
* Reuse the animation method for launching an AppPair icon from taskbar
by specifying which windowing mode to look for if we're launching the
actual split pair vs just one in fullscreen

Bug: 323089902
Test: Launches fine visually
Change-Id: I415343a48e980afd7f4e511558d350cf15b97ca1
Merged-In: I415343a48e980afd7f4e511558d350cf15b97ca1