Upgrade to Dart 3.5

[athomas]

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[copybara-service]

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[copybara-service]

https://dart-review.googlesource.com/c/homebrew-dart/+/388065 has been updated with the latest commits from this pull request.

[copybara-service]

https://dart-review.googlesource.com/c/homebrew-dart/+/388065 has been updated with the latest commits from this pull request.