Update mixin guidance on Effective Dart #4941
Description
Page URL
https://dart.dev/effective-dart/design#avoid-mixing-in-a-class-that-isnt-intended-to-be-a-mixin
Page source
Describe the problem
For compatibility, Dart still allows you to mix in classes that aren’t defined using mixin.
I don't think that's the case now. The purpose of adding mixin classes was to no longer have this ambiguity.
Expected fix
Rewrite the section, or more likely remove it, or maybe replace it with different guidance e.g. "DO use a mixin class to..."
Additional context
No response