Add "Swift Package Manager Support" Tag for Flutter Packages

[ricardodalarme]

Description

With Flutter's new support for Swift Package Manager (SPM), it would be helpful to identify packages on pub.dev that already support SPM. Adding a specific tag like "Swift Package Manager Support" to these packages would make it easier for developers to find and utilize them.

Proposal

1. Add functionality to pub.dev to automatically identify if a package supports Swift Package Manager.
2. Once identified, pub.dev should automatically add a "Swift Package Manager Support" tag to the package's page.

This would be a small but valuable addition to improve discoverability and adoption of SPM-compatible packages within the Flutter ecosystem.

[sigurdm]

Try: https://pub.dev/packages?q=is%3Aswiftpm-plugin+

[sigurdm]

Related to dart-lang/pana#1402

[sigurdm]

(We still haven't decided how we want to surface this)