Add IS_READ column in call log and voicemail providers.

Initially we had exposed NEW in the voicemail provider instead of the
IS_READ field. However, NEW is already used in the call log to represent
a missed call for which a notification needs to be shown to the user.

On the other hand, voicemail need both be shown in a notification and
retain their own read/unread state, which is determined by whether the
user has opened the details of the voicemail.

This change introduces the IS_READ field for voicemails and exposes it
also via the call log content provider.

The NEW column in the voicemail content provider will be removed in a
follow-up.

Bug: 5036195
Change-Id: I2f8c04685a82cbf77f4778cf057ff62c7da1256a