Add hints in Overview

If the ENABLE_HINTS_IN_OVERVIEW flag is enabled, pulls chip hint
data (currently from the NavBarHint plugin; eventually from AiAi)
and shows the chips between the task view screenshot and the QSB.

Screenshot: https://screenshot.googleplex.com/Ww05W13XjBv

BUG:124390101

Change-Id: I7686673b705257eca31f2fa40e2744e197153c7c