DO NOT MERGE: unrevert "Force FGS notifications to show for a minimum time"

See CL with change id (I0680034ed9315aa2c05282524d48faaed066ebd0) for
the meaningful changes/description. This change was reverted in qt-qpr1-dev
in order to fix a bug but never got unreverted due to the qt-dev CL
having the same change-id as the reverted one.

Bug: 119041698
Test: atest NotificationManagerServiceTest
Test: atest ForegroundServiceNotificationListenerTest
Change-Id: I50f16072b0e56ab69aabf8010ffffd172ca7c05a