Also includes drive-by when I subbed `@default` (not valid) to
`@defaultValue` (valid!) in a few places and exposed types from
`Coverage.ts` so they get exposed too.
Fixes 6876.
These files will be used by both the web and node versions of Puppeteer.
Another name for this might be "core" but I don't want to cause
confusion with the puppeteer-core package that we publish at the moment.