Implement VoicemailDataSource

This data source determines if the call is to the voicemail inbox.

isVoicemail() is removed from NumberAttributes and PhoneLookup. It is yet decided how in call UI should handle voicemail calls in the future.

TAG_CHANGE_OK=proto not in prod yet. Please clear app data.
TYPE_CHANGE_OK=above
Bug: 70989587
Test: Unit tests
PiperOrigin-RevId: 189650273
Change-Id: Iafebf1abb18c74301b62a72d1d04deecd6d78d29