Add comments for suppressed warnings

[zeitlinger]

#7833 already started to add warnings, but it turned out to be a huge PR.

Instead, we can tackle adding comments on a per module level.

[Gosling-dude]

I can take this up and add concise comments explaining suppressed warnings on a per-module basis, keeping the scope intentionally small as suggested here. Let me know if that works.

[zeitlinger]

It would be good to change the tooling to make sure an entire module is covered, e.g. by adding a property to the build file.