Refactor Power Usage Time Page.

- Show use time category

Screenshot:
[Screen time with hint] https://screenshot.googleplex.com/3cRLrwevzw4iytb
[Background time with hint] https://screenshot.googleplex.com/zEf8PcWopCVCRZR
[without hint] https://screenshot.googleplex.com/9bao9sVd8s7VRwM
[enter from app info (without category)] https://screenshot.googleplex.com/8sozxMrq8ojadiF

Bug: 302063050
Test: Manual
Change-Id: Ic967d05a173afa76c2a958e1332dedd9f83cd687