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: TeleServiceTests
Merged-In: Ia996798cc3e0d1fee82f32365d53876dee572579
Change-Id: I448f7e521acb06bdb8c59030b1de4b9dc6006ae4