HeadsUpCoordinatorTest: Factor out some methods

To make the transition from the NotificationInterruptStateProvider
interface to the VisualInterruptionDecisionProvider interface smoother,
factor all the calls into those classes out into a few methods.

Bug: 261728888
Test: atest HeadsUpCoordinatorTest
Change-Id: I19407258a503065cfe14ddc941b723e21bc148d9