Do not add __typename to @client selection sets @export-ed as input variables.

[benjamn]

Fixes #4691.

[benjamn]

@OurMajesty @supercranky Does the test included in this commit capture your use case(s) from #4691?

[benjamn]

@hwillson Should this test be stricter? For example, we could require that the directive has an as argument that refers to a declared variable.

[hwillson]

@benjamn I think it's okay like this. If we need to change this in the future, we should be able to pretty easily.

[Jayphen]

This does not work in the case where the field contains nested fields:

filters @client @export(as: "filters") {
  priceFilters {
    value
  }

The typename will be removed from filters, but not from priceFilters.

I have been using this workaround, but it seems undesirable:

filters @client @export(as: "filters") {
  priceFilters @export {
    value
  }

[hwillson]

Looks great @benjamn - thanks!

[OurMajesty]

@OurMajesty @supercranky Does the test included in this commit capture your use case(s) from #4691?

Here's the exact request from the real application that caused the error:

#import 'graphql/fragments/Attachment'
#import 'graphql/fragments/Product'

query GetProducts($filter: ProductFilter, $limit: Int!, $offset: Int!) {
    currentFilter @client @export(as: "filter") {
        active
        recursiveCategoryId
        state {
            in
        }
        valid
    }
    productList(filter: $filter, limit: $limit, offset: $offset) {
        totalCount
        resultList {
            ...ProductFields
            client {
                id
                inn
                kpp
                name
                clientName @client
            }
            images {
                ...AttachmentFields
            }
        }
    }
}

I don't think it have important differences, but maybe it's helpful.