Expose printDirective function to enable schema sharding (#3822)

Author: tomgasson

src/index.ts

@@ -428,6 +428,8 @@ export {
   printSchema,
   // Print a GraphQLType to GraphQL Schema language.
   printType,
+  // Print a GraphQLDirective to GraphQL Schema language.
+  printDirective,
   // Prints the built-in introspection schema in the Schema Language format.
   printIntrospectionSchema,
   // Create a GraphQLType from a GraphQL language AST.

src/utilities/index.ts

@@ -49,6 +49,7 @@ export { lexicographicSortSchema } from './lexicographicSortSchema.js';
 export {
   printSchema,
   printType,
+  printDirective,
   printIntrospectionSchema,
 } from './printSchema.js';
 

src/utilities/printSchema.ts

@@ -268,7 +268,7 @@ function printInputValue(arg: GraphQLInputField): string {
   return argDecl + printDeprecated(arg.deprecationReason);
 }
 
-function printDirective(directive: GraphQLDirective): string {
+export function printDirective(directive: GraphQLDirective): string {
   return (
     printDescription(directive) +
     'directive @' +