Expose getArgumentValues as public API

Fixes graphql#2719

Author: IvanGoncharov

src/execution/index.ts

@@ -15,4 +15,4 @@ export type {
 
 export { subscribe, createSourceEventStream } from './subscribe';
 
-export { getDirectiveValues } from './values';
+export { getVariableValues, getDirectiveValues } from './values';

src/execution/values.ts

@@ -35,8 +35,6 @@ type CoercedVariableValues =
  * Note: The returned value is a plain Object with a prototype, since it is
  * exposed to user code. Care should be taken to not pull values from the
  * Object prototype.
- *
- * @internal
  */
 export function getVariableValues(
   schema: GraphQLSchema,

src/index.ts

@@ -318,6 +318,7 @@ export {
   defaultFieldResolver,
   defaultTypeResolver,
   responsePathAsArray,
+  getVariableValues,
   getDirectiveValues,
   subscribe,
   createSourceEventStream,