Add OngoingCallInteractor

This CL removes dependency on OngoingCallController by introducing OngoingCallInteractor as the source of truth for ongoing call state.

The interactor:
Reads call notifications from ActiveNotificationsInteractor
Tracks call app visibility through ActivityManagerRepository
Emits ongoing call state through a Flow to CallChipInteractor


Bug:b/372657935
Flag: com.android.systemui.status_bar_chips_modernization

Change-Id: Ifd5ae9c3e566b99f268201f03db092850923eee6