Rewriting phone constants for mainline

* Exposing Emergency extra constants through TelephonyManager
* Always reading or writing PhoneConstants.SubscriptionKey
with SubscriptionManager.EXTRA_SUBSCRIPTION_KEY

Bug: 147465477
Test: FrameworksCoreTests, FrameworksServicesTest, CarrierTests
Change-Id: I84d6687ca6cab86c8c68dc2dd2679cfee0919c1e