Add Hotseat items to Taskbar

- Currently supports WorkspaceItemInfo (e.g. normal app icons
  including hotseat predictions and pinned deep shortcuts).
- Currently doesn't support Folders, Notification dots, or
  long press.

Some technical details:
- Always allow HotseatPredictionController updates given the
  Hotseat is always showing even when Launcher is stopped.
- Represent Taskbar Hotseat items as BubbleTextViews, to
  allow for normal click handling etc. When the hotseat is
  updated, we reuse the same BubbleTextViews that were
  initially inflated, and just reapply the new info.
- Add new BubbleTextView iconDisplay for Taskbar, to allow
  for different treatment such as icon size.

Bug: 171917176
Change-Id: I325eb39051f2dc69228b39b5c40ed0cbdad8e200