Add Telephony intent class to public API.

Remove @hide from android.provider.Telephony for K release for
SMS and MMS related tables, and APN database (for MMSC info).
Helper methods are hidden except for two that use non-public APIs.

Bug: 10653081
Change-Id: I3509b122ae4e762c1c44e6b4aa8b36c8d0b62224