fix(federation): add reference resolver type to resolver map

Fixes #2205 by adding a type definition for `__resolveReference`
to the existing `GraphQLResolverMap` interface.

Author: hvolschenkcb

subgraph-js/src/schema-helper/resolverMap.ts

@@ -1,4 +1,5 @@
 import { GraphQLFieldResolver, GraphQLScalarType, DocumentNode } from 'graphql';
+import type { GraphQLReferenceResolver } from '../schemaExtensions';
 
 export interface GraphQLSchemaModule {
   typeDefs: DocumentNode;
@@ -8,15 +9,17 @@ export interface GraphQLSchemaModule {
 // eslint-disable-next-line @typescript-eslint/ban-types
 export interface GraphQLResolverMap<TContext = {}> {
   [typeName: string]:
-    | {
+    | ({
         [fieldName: string]:
           | GraphQLFieldResolver<any, TContext>
           | {
               requires?: string;
               resolve?: GraphQLFieldResolver<any, TContext>;
               subscribe?: GraphQLFieldResolver<any, TContext>;
             };
-      }
+      } & {
+        __resolveReference: GraphQLReferenceResolver<TContext>;
+      })
     | GraphQLScalarType
     | {
         [enumValue: string]: string | number;