Telecom API updates for mainline support.

Moving some Telecom APIs into public since they are harmless to expose.
Moving some other Telecom APIs into the System API space since they're
API details specific to the TelephonyConnectionService so don't need to
be exposed in the public API.

Bug: 141576016
Test: Manual smoke test.
Test: Run unit tests.
Test: Run CTS tests.
Change-Id: Iaf75b9d671712d791f501c11536e73436908f7de
Merged-In: Iaf75b9d671712d791f501c11536e73436908f7de