Status Bar - Extract interfaces of initialization related classes

This will allow to have different implementations of these interfaces.
It will be needed for multi display support, where we will have
multi display specific implementations.

Test: Build and run SystemUI
Flag: EXEMPT no changes. Just extracting classes into interfaces.
Bug: 367592591
Change-Id: Iec0984d423b60b851f34f1da9441a2eea7fb3fc3