add rudimentary typing to default_field_resolver

[hoefling]

It's me again with a type hints issue. I'm writing a custom field resolver:

def custom_field_resolver(source: Any, info: GraphQLResolveInfo, **args: Any) -> Any:
    if info.field_name == "foo" and hasattr(source, "bar"):
        return source.bar
    return default_field_resolver(source, info, **args)


result = await graphql_execute(
    ...,
    field_resolver=custom_field_resolver,
)

and have disallow_untyped_calls = True in my mypy config. Running the type check yields

<mymod>.py:<line>: error: Call to untyped function "default_field_resolver" in typed context

I'd thus propose to add at least a rudimentary typing to graphql.execute.default_field_resolver for now. Once Python 3.6 and 3.7 are dropped, I suppose a better typing using protocols could be possible.

Signed-off-by: oleg.hoefling oleg.hoefling@gmail.com

[Cito]

LGTM, thank you. I have created #89 to solve this more radically in the long run.