Ignore nested keyboard navigation clusters

Keyboard navigation clusters should not be nested; however,
if they are, the behavior is to pretend like they aren't
clusters. This includes ignoring the keyboardNavigationCluster
+ touchscreenBlocksFocus combo altogether.

Bug: 32804858
Test: Added some nested cluster scenarios to ViewGroupTest CTS
Change-Id: I776942842b8c1147200fc39f7eacca493e37c20c