Improve rect-level focus ordering

Previously views were ordered strictly by their tops. This
lead to many cases of tab-focus moving "backwards". For example
a horizontal row of views with different heights would not
always move start-to-end.

Bug: 34854951
Bug: 33848452
Test: Run against UX-provided localized focus-orders to make sure
      it improves behavior. Added a sanity-check CTS test for
      well-behaved (simple) layouts.

Change-Id: I5b01a301e0bbcbcad472ffdb26ebf4fbb6380756