Formalize CallDirection APIs

Promote Connection#getCallDirection into a proper system API as part of
Telecom internal mainline prep (used by Telephony to get call direction
of the connection).

Bug: 322514233
Bug: 311773409
Test: atest ConnectionServiceTest
Change-Id: I36acd83503148a7919518dd26f06d5aca0b49b86
2 files changed