Also recreate astNode for fields (#580)

* Also recreate astNode for fields

In a [previous commit](fd9f626) we added the `astNode` property in the `reacreateCompositeType` function. That resulted in cache control working with schema stitching but only for GraphQL Types. By recreating the `astNode` prop also in `fieldToFieldConfig` cache control also works for fields. This is required for caching fields and hence queries.

* Add ast to input field node too

Author: BassT

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### vNEXT
 
+* Also recreate `astNode` property for fields, not only types, when recreating schemas. [PR #580](https://github.com/apollographql/graphql-tools/pull/580)
 * Fix `delegateToSchema.js` to accept and move forward args with zero or false values [PR #586](https://github.com/apollographql/graphql-tools/pull/586)
 
 ### v2.18.0

src/stitching/schemaRecreation.ts

@@ -92,6 +92,7 @@ function fieldToFieldConfig(
     resolve: defaultMergedResolver,
     description: field.description,
     deprecationReason: field.deprecationReason,
+    astNode: field.astNode,
   };
 }
 
@@ -140,5 +141,6 @@ function inputFieldToFieldConfig(
     type: registry.resolveType(field.type),
     defaultValue: field.defaultValue,
     description: field.description,
+    astNode: field.astNode,
   };
 }