Use Telecom API for checking if a number is voicemail (2/2)

Since we don't want to communicate directly with Telephony in dialer,
call
PhoneNumberUtils.isVoiceMailNumber (a Telephony method) through the
Telecom API. Add a method in TelecomManager to do this.

Bug: 17925501

Change-Id: Id1e5824f27ef40f64b8a03ee912d82d1cc5324ac