Generated visitors are not generic on returned type

[gsilvasimoesPT]

Visitors are generated like this:

class Visitor:
    @abstractmethod
    def _variant_a(self, variant_a: "VariantA") -> Any:
        pass

    @abstractmethod
    def _variant_b(self, variant_b: "VariantB") -> Any:
        pass

It feels possible to define something like:

class Visitor(Generic[T]):
    @abstractmethod
    def _variant_a(self, variant_a: "VariantA") -> T:
        pass

    @abstractmethod
    def _variant_b(self, variant_b: "VariantB") -> T:
        pass

and also potentially make it backwards compatible.