Add VisualVoicemailService

VisualVoicemailService can be implemennted by the default dialer to
provide a visual voicemail client similar to the OMTP visual voicemail
spec.

Other APIs such as the SMS filter and hidden text SMS sending are made
public and consolidated into the service interface.

Test: make. CTS tests in a follow up CL
Change-Id: Ib5e9aa15fc098f4c13b15e5dbecf9ab646e0e400
Merged-in: Ib5e9aa15fc098f4c13b15e5dbecf9ab646e0e400