[SB][Chips] Add TimeSource to ShortTimeDelta for chip model.

We need to pass a fake time source in the view model to make it easy to
set a fake time in tests.

Bug: 404502700
Flag: com.android.systemui.status_bar_chips_modernization
Test: Post promoted notif for 5 minutes in future -> verify chip says
"5min" and counts down to 4min, 3min, 2min, 1min, now
Test: Post promoted notif for over an hour in future -> verify chip says
"1hr"
Test: Post promoted notif for now -> verify chip has no text
Test: Post promoted notif for time in past -> verify chip has no text

Change-Id: I9dcedbb3cc483ac5b254a51a84dc40c092c9db4f