Implement getVisualVoicemailPackageName()

Bug: 32414216
Test: cts test android.provider.cts.VoicemailContractTest
    android.telephony.cts.VisualVoicemailServiceTest

Change-Id: I5e9c295256833f9d33513b2e834b0c5c3c929d4b
Merged-in: I5e9c295256833f9d33513b2e834b0c5c3c929d4b
2 files changed