stubgen (stubgenc): Support for __new__ in C types

Feature

Implement support for __new__ in mypy.stubgenc.generate_c_type_stub

Pitch

Currently, there is a # TODO: We should support __new__. in mypy.stubgenc.generate_c_type_stub.
AFAIK, C extensions autogenerate the docstring Create and return a new object. See help(type) for accurate signature. for the __new__ / __init__ attributes of C type objects and I am not aware of a way to customize this.
Therefore, my proposal would be to use the docstring of the C type itself and scan for TypeName(...) (if TypeName is the name of the C type) and pass this to infer_sig_from_docstring.
Not sure if TypeName(...) should be required to include self / cls or if such an argument should be made optional (automatically add self to the signature of __init__ if it is missing in TypeName(...)).

I would offer to implement this, if we could specify the desired behavior.

Inizia da mypy.stubgenc.generate_c_type_stub e leggi come gestisce attualmente gli attributi dei tipi C e come chiama infer_sig_from_docstring. Chiarisci il parsing previsto e il comportamento di self/cls per TypeName(...) prima di implementarlo. Il lavoro è completato quando gli stub dei tipi C generati includono le firme concordate di new e init, derivate dalla docstring del tipo.