Allow to register new class/dataclass/attribute makers in attrs plugin

This is a feature request.

attrs is very much intended to be composable (e.g. https://github.com/hynek/environ_config) but currently the attrs plugin only works on the core library's functions: https://github.com/python/mypy/blob/b2d61741623f2a0573f2b1bdb8391ceed862cf69/mypy/plugins/attrs.py#L24-L37

I would like to be able to signal somehow to mypy, that some function is a wrapper around @attr.s/@attr.ib/@attr.dataclass. Not only would third-party applications benefit, but I could really use it while experimenting on https://github.com/python-attrs/attrs/issues/408.

Any ideas/plans how we could achieve that?

cc also @euresti & @chadrik

Comienza con mypy/plugins/attrs.py, especialmente con las funciones de la biblioteca principal enumeradas alrededor de las líneas 24–37, y sigue cómo el plugin de attrs reconoce @attr.s, @attr.ib y @attr.dataclass. Revisa la issue enlazada de attrs para conocer el caso de uso motivador de los wrappers. Se considera terminado cuando exista una forma documentada y probada para que los wrappers de terceros registren un comportamiento equivalente para clases, dataclasses o creadores de atributos.