Refactor background optimization mode in Power Usage Detail page.

[Screenshot]:
before: https://screenshot.googleplex.com/6m5jYWHofY2pFov

after:
[App battery usage]
- [normal] https://screenshot.googleplex.com/7aurWk7cHKaWds7
- [always unrestried/optimized] https://screenshot.googleplex.com/3rGAh4ccUYTKBAr

[Allow Background usage]
- [Restricted]: https://screenshot.googleplex.com/MPXjQe5kPWw2nhr
- [Optimized]: https://screenshot.googleplex.com/6w4zTT6r34APnGc
- [Unrestricted]: https://screenshot.googleplex.com/97FgvHWMrwASqYH

Bug: 302063050
Bug: 306295660
Bug: 308359833
Test: manual
Change-Id: I3237d015549fe26e62d6d68c13403cc2cbdf0017