Fixed default-cluster and empty-cluster navigation behavior

Cluster navigation would get stuck if:
 - there was an empty cluster (nothing to focus)
 - there were views NOT in a cluster and the global
   default-focused view was in a cluster.

This will skip over empty clusters during cluster navigation
and when the default "cluster" is active, it will try to
focus a non-clustered focusable instead of the global default
(and if there aren't any non-clustered focusables, it will
skip over the default "cluster" as it now does with actual
clusters.

Bug: 35273052
Bug: 34361282
Test: Added/Updated CTS tests and checked behavior in a test app.
Change-Id: I0b4d55707203f6a0453f25313f940927d59a9b31