New API to specify accessibility focus grouping

We've been telling developers to use the focusable
attribute to control grouping for accessibility focus. This
new API can be used in place of the focusable attribute.

Bug: 63889180
Test: Adding new CTS tests for new api.

Change-Id: I5cbeb736a3b206f87aa3d921a39c43861c7ff082
6 files changed