Create return-to-home app widget animation

If an app has been most recently launched from an app widget, when
swiped away, the app animates to the widget's position.

This is done by attributing the app launch to the widget through
the ActivityOptions's launch cookies, and using a FloatingWidgetView
throughout the animation.

Bug: 169042867
Test: manual
Change-Id: I24c2623b5b3407504a4768b076849c47f73cbae0