Automate releasing and publishing #358
Description
Package
All packages
What happened?
Releasing is currently highly manual, https://github.com/material-foundation/flutter-packages/blob/main/CONTRIBUTING.md#releasing, pending clarity on dart-lang/setup-dart#68 and on a broader flutter solution.
Once a an ideal solution is available, we should fix .github/workflows/publish.yaml.
An ideal solution might be something in the vein of https://github.com/marketplace/actions/dart-and-flutter-package-publisher, but waiting to see if there's something "official" from Flutter.