[Not to land] Test with Hierarchical Focus

[yschimke]

WHAT

Test with Hierarchical Focus.

Test only, we should deprecate existing methods and define new ones.

WHY

Better expression of focus than lifecycle.

HOW

Implement hooks in PagerScreen and WearNavScaffold

Checklist :clipboard:

• [ ] Add explicit visibility modifier and explicit return types for public declarations
• [ ] Run spotless check
• [ ] Run tests
• [ ] Update metalava's signature text files