Long-press on an app to reveal its shortcuts.

- Add ShortcutsContainerListener to icons on workspace, folders, and
  all apps. This handles long-press and forwards following touches to
  the DeepShortcutsContainer that is created.
- Drag over shortcut before lifting finger to launch it.
- Shortcuts are rendered in pill-shaped DeepShortcutViews,
  which are inside DeepShortcutContainer on DragLayer.
- The shortcut container orients above or below the icon, and left or
  right-aligns with it. Biases for above + left-align.
- Long press a DeepShortcutPill to drag and pin it to the workspace.

Bug: 28980830
Change-Id: I08658d13ae51fe53064644e8d8f7b42f150fdd7d