cocoon scheduler dart project

[CaseyHillers]

• Create scheduler dart project
• Move scheduler validation logic out of app_dart/lib/src/service/scheduler.dart to scheduler/lib/scheduler.dart
• Move scheduler protos from app_dart to scheduler
• Move ci.yaml validation script from app_dart to scheduler
• Import scheduler into app_dart

Issues

flutter/flutter#82072

[jonahwilliams]

If you're moving code from app_dart to a dependency on app_dart, i don't think that will change the calculus on version solving at all

[CaseyHillers]

If you're moving code from app_dart to a dependency on app_dart, i don't think that will change the calculus on version solving at all

My understanding from the recipe (an example run at https://ci.chromium.org/ui/p/flutter/builders/prod/Linux%20validate_ci_config/373/overview) is this would checkout cocoon, but only run pub get on the scheduler project

\cc @christopherfujino who wrote the recipe can verify

[jonahwilliams]

I guess that would definitely help the problem, but we'd eventually need to get all of the versions bumped anyway

[jonahwilliams]

LGTM