Improvements to LINT_IMPLICIT_VISIBILITY
Summary: See D10687#104589.
Test Plan: Wrote unit tests.
Reviewers: richardvanvelzen, epriestley, Blessed Reviewers
Reviewed By: richardvanvelzen, epriestley, Blessed Reviewers
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D11267