Update generated code formatting to dart 3

[qwezey]

Changing Version(2, 12, 0) to DartFormatter.latestLanguageVersion causes tests to fail: test.log

functional_widget/packages/code_gen_tester/lib/src/tester.dart

Line 68 in 6e67697

final formatter = DartFormatter(languageVersion: Version(2, 12, 0));

It seems the generator needs to be updated for the new formatting.

[rrousselGit]

More importantly, all tests need to be rewritten to not rely on what the generated code. Cf Freezed/Riverpod's tests.

That's one of the main reason I haven't worked much on this project. I can't be bothered updating the tests 🙈