Update generated code formatting to dart 3

[qwezey]

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

https://github.com/rrousselGit/functional_widget/blob/6e676977e53258f3aa5604927df3abde31939089/packages/code_gen_tester/lib/src/tester.dart#L68

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 🙈