Converting widget panel into a floating view

> The widget panel is only inflated when needed
> Using the swipe up/down interaction for widgets tray
> Removing additional view wrappers from all-apps
> Widget tray is preserved across activity recreation
> Launcher no longer has WIDGET state, the actual code around
  the states will be removed in a follow-up cl

Bug: 67678570
Bug: 67585158
Change-Id: Ia29a7c33ec81e6c53cc24e2906b7022b6f41755b