Update VVM API

+ TelephonyManager.getVisualVoicemailPackageName() uses pinned subId
  from the manager.
+ TelephonyManager.getNetworkSpecifier() updated doc to explain what
  a network specifier is.
+ TelephonyManager.getCarrierConfig() Annotated with @WorkerThread
  specified failure behavior.
+ VisualVoicemailSms.getFields() Doc specified values are carrier
  dependent.

- Hide DEFAULT_* from VisualVociemaliSmsFitelrSettings

Test: CTS TelephonyManagerTest
Bug: 35766748
Fixes: 35766370
Fixes: 35766489
Change-Id: If48d48a0cf588bcb59c7b77ce6a452d2fda7bfa5
Merged-in: If48d48a0cf588bcb59c7b77ce6a452d2fda7bfa5