Change header background/text/icons color to be system based.

Uses system defined material attributes to determine colors for header
background and elements. Additionally, reduces opacity of foreground
elements based on focus status.

Video: http://recall/-/cQv7jbdYTSYnSPt2ZoXKaw/cLsUasu6Hpui1hk3ETKDrz
Bug: 312747815
Test: Manual
Change-Id: Ieecd7504c04b6d4cf62a2a2b694b1fcf2dfbd4bb