Upgrade to Dart 3.x

[aaronfranke]

Dart 3.x will be released very soon, mid-2023, with some compatibility-breaking changes.

We should look into upgrading the glTF validator to use Dart 3.x or else it will stop running on people's systems with only the latest Dart installed.

[aaronfranke]

@lexaknyazev Is glTF-Validator planned to be maintained? There have been no commits merged to the repo in 2 years, and it does not run on modern systems anymore due to Dart 3.x breaking compatibility.

[lexaknyazev]

@aaronfranke There will be a major update later this year.

[0b5vr]

fyi, I'm using Docker to build glTF-Validator with Dart 2 for now:

docker run -it --rm -v .:/app dart:2

cd /app
dart pub get
dart run grinder exe