Monitor long-running foreground services

If a certain package has foreground services running for a long time,
say the accumulated durations over last X hours are more than Y hours,
system will post a notification to remind the user.

Some type of apps are subjected to be exempted, i.e. if it's already
in the device idle allowlist. More exemption could be added in
the follow-up CLs.

Bug: 200326767
Bug: 203105544
Test: atest FrameworksMockingServicesTests:BackgroundRestrictionTest
Change-Id: I3a8f34c33e7a533240abc7cf4fa569a0956eec73