Use Telecom API for checking if a number is voicemail (1/2)

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: Iecea82a0e5f0b106eaf105e9026d606110acf122