[SB][Notif] Have notif chips be isHidden=true if app is visible.

Previously, if a notification's app was visible, we changed its model to
be OngoingActivityChipModel.Inactive. But there's 2 reasons I'd rather
model it as OngoingActivityChipModel.Active(isHidden=true):

1) For UiEvent metric logging, it's better to keep the chip as Active
   the entire time so that we don't log a "chip removed" event whenever
   the notification's app is open.

2) When we bring return animations to notification chips (b/202516970),
   we'll need to make this update anyway.

Bug: 202516970
Bug: 386821418
Fixes: 396636550
Bug: 364653005
Flag: com.android.systemui.status_bar_notification_chips

Test: Have status bar notification chip, then open app -> verify chip
still disappears. Close app -> verify chip still re-appears.
Test: atest StatusBarNotificationChipsInteractorTest
NotifChipsViewModelTest

Change-Id: I87af8943acc82989fb54c11660f222adcb49da0b