Migrate splitscreen to WM shell lib (2/n)

Removes Divider from SystemUI component list since it is no longer
needed after the split screen feature migrated to WM shell library.

Provides optional controller of split screen for sysui components to
use. Different varients of SystemUI could leverage dagger module to
decide whether to load the controller or not.

Implements WMShell component in SysUISingleton scope to help delegating
sysui specific events to WM shell controllers.

Detached DisplayImeController's initialization step from split screen
feature with the reason that some of SystemUI varients might not have
split screen feature.

Bug: 161116823
Test: atest SystemUITests
Test: atest SystemUIGoogleTests
Test: atest CarSystemUITests
Test: manual verified spliscreen behavior
Change-Id: I4220b5ce53bc7b793b95cfca34100e808b9f052c