Add visibility for core tests

Allow core tests to use hidden connectivity APIs. Benchmark tests in
particular cannot be run without these.

Ignore-AOSP-First: Avoiding merge conflicts, cherry-pick will follow
Bug: 197717846
Test: m
  (cherry-picked from ag/16772124)
Change-Id: Ia01f24317d14b063f9a7e24c3ada11b140641c50
Merged-In: Ia01f24317d14b063f9a7e24c3ada11b140641c50