[CS] 1/2: Rename NavBarController to NavBarControllerImpl.

The next CL will add an interface named NavBarController so that we can
provide a real implementation for SysUI and an empty implementation for
Arc. This CL just renames the implementation to preserve git history.

Bug: 277764509
Test: compiles
Change-Id: I25344d9a483d50d7974583823b9a3be8eceb9982
18 files changed