[SB][Chips] Use call chip helper in OngoingActivityChipsWithNotifsVMTest

Mostly, this actually involves adding helper methods for
ActiveNotificationListRepository to just add or remove notifications
instead of resetting the whole list each time. This is needed because
both the call chip and the notification chips come from notification
information, so we don't want to accidentally reset the call chip when
setting up notification chips and vice versa.

Bug: 372657935
Test: atest OngoingActivityChipsWithNotifsViewModelTest
Flag: com.android.systemui.status_bar_chips_modernization
Change-Id: I4451b1df194bebb2723c9662a50ab843bf4b2d36