Polish all apps taskbar unstash behavior for transient and persistent.

- During gestures from taskbar all apps, unstash immediately in
  transient.
- Overlay closes sooner if all apps is open (still done later for EDU).
- Taskbar stashes in overview when All Apps is opened.
- Transient app-window threshold is ignored if All Apps is opened.

Test: Manual
Fix: 262076812
Change-Id: I46b2dcdc75ee0cc15c1b47da2139ff8c20cf618a