Commit 1: Enable lint check for comments
Part of #217. Follow up from #1982 and #2018.
A subsequent commit will fix the ci failure.
Commit 2: Address all comment-related linter errors.
This change addresses all comment-related linter errors by doing the
following:
- Add comments to exported symbols
- Make some exported symbols private
- Recommend via TODOs that some exported symbols should should move or
be removed
This PR does not:
- Modify, move, or remove any code
- Modify existing comments
Signed-off-by: Andrew Seigner <siggy@buoyant.io>