"Dart 3 ready" badge on pub.dev

[jonasfj]

Requires a full analysis using a Dart 3 alpha release to pass in pana.
This means doing the analysis twice, maybe not running all of pana, but having pana run dart analyze twice.

Unknown: We need to get hold of a Dart 3 alpha or dev release a few weeks before it's shipped.

[jonasfj]

Blocked on dart-lang/pana#1123

[jonasfj]

We probably need to launch with this a dev-release, and keep the badge behind experimental. We can even use Dart 2.18, so that we just switch the SDK when we have the alpha release ready.

[mit-mit]

Versioning CL is https://dart-review.git.corp.google.com/c/sdk/+/271922?usp=search

[mit-mit]

This is currently blocked by dart-lang/sdk#50694

[mit-mit]

Badges are live; closing