Create AppForegroundHelper

Create a new helper to deal with application foreground state changes.

1) Rename various Helpers.
2) Move GnssManagerService into location dir.
3) Use new AppForegroundHelper everywhere.
4) Move sendNiRequest to internal API
5) Some refactoring of NetInitiatedActivity

Test: atest AppForegroundHelperTest
Change-Id: Ifffe0e6a34452a18d017c6b190547b904d77b430