Repointed subscription ids to subscription info

TelephonyManager.getActiveSubscriptionIds is a hidden API, changed to info.
Exposed subscriber id in TelephonyManager as getSubscriberId().
Made revisions to NetworkPolicyManagerServiceTest to account for changes.

Bug: 146174645
Test: FrameworkServiceTests
Change-Id: I591f750bbcbdf2c4b97caff76fd31cec28a56e73