Make StatusBar purely optional

To be able to inject Optional.empty() to Optional<StatusBar>, this CL

 - removes raw StatusBar references and replaces it with Optional<StatusBar>
 - replaces Optional<Lazy<StatusBar>> to Lazy<Optional<StatusBar>>

Bug: 144309772
Bug: 138625582
Bug: 187111275
Bug: 187111293
Test: atest SystemUITests
Change-Id: I07b63e417dd4cc75a17951619065ba0f234bc2aa
Merged-In: I07b63e417dd4cc75a17951619065ba0f234bc2aa