Add voicemail permissions as pre-granted permissions for ROLE_DIALER.

Adding READ and WRITE voicemail permissions.
This is used by all dialer apps to be notified of incoming voicemails.
Adding as a pre-grant to the app holding the default dialer role.

Test: Add CTS test to verify grant of permission.
Bug: 149731110
Change-Id: If7e4bb3f55ba126a2d5c8f5f4dbaa3d7fd8ece12