fix(core/bindings): Fix conditional/optional variables type based on TypedDocumentNode generic

[kitten]

Resolves #2668

Summary

Previously, we had a couple of cases that wouldn't allow us to correctly identify when the variables input should be optional, e.g. allowing for:

import { useQuery, TypedDocumentNode } from 'urql';
const x: TypedDocumentNode<{ data: null }, { test: string | null }> = {} as any;
useQuery({ query: x });

Additionally, it wasn't always easily possible to proxy generic inputs to our hooks and bindings, e.g. allowing for:

import { useQuery, TypedDocumentNode, AnyVariables } from 'urql';

export function wrapper<Data, Variables extends AnyVariables = AnyVariables>(
  query: TypedDocumentNode<Data, Variables>,
  variables: Variables,
) {
  return useQuery({ query, variables });
}

This is now resolved and to prevent future mistakes a GraphQLRequestParams utility type has been exposed by @urql/core which will be maintained/exposed as a public type, but is also reused in all of our bindings.

NOTE on patch: This is a patch and not a major/breaking change since we can never break types by making a property optional rather than required. Since we're a) widening the type with the union, and b) fixing cases where variables should be optional, this shouldn't break any TS types.

Set of changes

• Add GraphQLRequestParams utility fixing optional variables
• Update bindings to use GraphQLRequestParams where query, variables inputs are accepted