Unhide telecom APIs needed by Contacts

* Removed @SystemApi and @hide from some telecom classes
  and APIs
* Stopped using explicit @link's to ConnectionService, so
  that I didn't need to unhide ConnectionService
* Added @SystemApi to hidden methods inside classes that
  I removed @SystemApi from.
* Ran update-api. This picked up unrelated Math changes
  from b/11388705.

Unbundling

Bug: 18777272
Bug: 11388705
Change-Id: I218e0c3c0ae515d3deb2d3b67657db45a0bad999