Generated API reference points to invalid links for Flutter/Dart classes leading to 404s

[sigurdm]

Copied from: flutter/flutter#170868

Steps to reproduce
The generated API reference for packages seems to have a number 404s referencing invalid pages for Flutter/Dart classes. This was picked up from a review of API ref for arcgis_maps but seems to apply to any generated API ref - here are a few examples from "Flutter Favorite" packages:

https://pub.dev/documentation/path_provider/latest/path_provider/
E.g. click on Future referenced from various functions
https://pub.dev/documentation/provider/latest/provider/StreamProvider-class.html
E.g. click on Stream referenced in the doc
https://pub.dev/documentation/firebase_core/latest/firebase_core/Firebase-class.html
E.g. click on Future referenced in the methods
This doesn't seem to affect all/most classes, but from our review it has at least affected references to Future, Stream, and Color.

References to Future go to https://api.flutter.dev/flutter/dart-core/Future-class.html instead of https://api.flutter.dev/flutter/dart-async/Future-class.html

References to Stream go to https://api.flutter.dev/flutter/dart-core/Stream-class.html instead of https://api.flutter.dev/flutter/dart-async/Stream-class.html

References to Color go to https://api.flutter.dev/flutter/painting/Color-class.html instead of https://api.flutter.dev/flutter/material/Colors-class.html

Has anyone else seen this? Is this likely a doc generator issue? Or anything configuration wise at the package level?

Expected results
All API references go to the correct, corresponding page.

Actual results
Some API references are hitting invalid pages / 404.

Code sample
Code sample
n/a - see link examples above

Screenshots or Video
Screenshots / Video demonstration
n/a

Logs
Logs
n/a

Flutter Doctor output
Doctor output
n/a

[sigurdm]

Is also a problem when the reference goes to api.dart.dev https://pub.dev/documentation/retry/latest/retry/