Fade deep shorcuts in and out.

Animate open:
- Stagger-fade shortcuts as they open
- Become fully opaque before fully open, at which point the
  arrow animates in (scale). This way there is no overlap of
  a translucent shortcut over an opaque arrow.

Animate close:
- Stagger-fade shortcuts as they close
- Delay fade until arrow animation is finished, to ensure
  there is no overlapping of translucent and opaque.

This is much less visually jarring when quickly dragging
and dropping apps with shortcuts.

Bug: 31533078
Change-Id: I8673ee64e92414c718233ea89b70362187e53696