Add a Telephony Debug Surface

This commit adds a small surface to allow telephony
to generate events for an external logger to capture
and use to take action such as gathering bugreports
or proprietary logs.

The event-IDs are considered non-stable, so they may
change from release to release or device to device.

Bug: 120941729
Test: manually tested by modifying Settings. Further
      tests will require the creation of a package
      that has READ_PRIVILEGED_PHONE_STATE.
Change-Id: I6360dab2d997d518ebd5f38a72fe88801e693bb7