CallDiagnosticService API

The CallDiagnosticService API is an OEM-backed API which allows an OEM
provided app to monitor the state of ongoing telephony calls on the
device and to help the user navigate connectivity or audio issues
related to these calls.  It also provides a means for the app to send
and receive device to device messages between devices during an ongoing
call (where supported) in order to facilitate a better calling experience.

Test: Added new CTS test suite for API.
Test: Manual test of CDS behavior using telecom command line option to
override the active CDS to the telecom test app implementation.
Bug: 163085177

Change-Id: I1f37408d2aa6c630f0f9e3d6b6eb8a390d804d7e