Add support for skipping call filtering

This CL adds support for recognising the constant:
  PhoneAccount.EXTRA_SKIP_CALL_FILTERING

If the extra is specified to be true, this:
  - Enforces that the phone account belongs to a system app
  - Skips call filtering when new calls are added

Bug: 65223222
Test: tested locally with modified ConnectionService
Test: ran unit tests: runtest --path packages/services/Telecomm/tests
Change-Id: I78029e98df53dd73eb422031dc5fe7036c838ef7