Fix date picker color handling, expose StateSet utils in more places

Enabled use of color selectors for the day number text, which lets us
use the "activated" text color and push the selection background
opacity up to 100%. Also ensures the selector circle stays within the
bounds of the selected day.

BUG: 18864682
Change-Id: Ia36ea748f83e13683a1de8ac1a259d353578d61a