Resolver.resolve_filename() missing

[trevor87]

class Resolver is missing the method resolve_filename().

As I am unsure, how to correctly type filename, I did not submit a PR. Instead, here is my current workaround:

In etree.pyi I added the following to class Resolver:

    def resolve_filename(
        self, filename: Any, context: Any)
    ): ...

Edit: Also, there is a return type. The documentation says "Return the name of a parsable file as input document." Does this mean that return type would be str?