*) Introduce LineageStatusBarItem class that contains interfaces
and utility methods that can be used by status bar items that
that are hosted here in the lineage-sdk in order to communicate
with systemui.
*) Nested interface: Manager
Implemented by layout view LineageStatusBarItemHolder in systemui.
Contains methods that are used to request receipt of certain
systemui events.
*) Nested interface: DarkReceiver
Can be used to listen for systemui DarkReceiver events.
*) Nested interface: VisibilityReceiver
Can be used to listen for changes in visibility of a statusbar item.
Works even if the statusbar item sets it's own visibility to GONE.
*) Util method: findManager(View v) walks up through parent views to
look for something that implements Manager.
*) Systemui side that provides a layout that implements Manager:
https://review.lineageos.org/#/c/202265/
Change-Id: Ie237db5bfac9994b87de39372505cd61c39d89ee
27a44cc178