Pubdev: load authors from API instead of pubspec.yaml
The Pubdev loader currently uses intrinsic metadata (
pubspec.yaml) to populate the revision author field.
The documentation discourages that: https://dart.dev/tools/pub/pubspec#authorauthors
However, it does not point to an API where we can get this info. We need to check how we can get it
Migrated from T4628 (view on Phabricator)