Use merged NetworkTemplate to query data usage

This CL uses merged NetworkTemplate so that it shows correct
data for carrier which is a virtual that has multiple
subscriberId under the hood.

By doing this, this CL also adds several hidden API so settings
can query by NetworkTemplate directly.

Fixes: 120566366
Test: RunSettingsLibRoboTests
Change-Id: I8b747697933c75b48b14387adafb5ac9ca165926