Centralize operation hashing function

These two operations will likely be used in tandem, and we want this to be consistent across consumers.

packages/apollo-graphql/src/index.ts

@@ -1 +1,4 @@
-export { defaultEngineReportingSignature } from "./signature";
+export {
+  defaultEngineReportingSignature,
+  hashForOperationSignature
+} from "./signature";

packages/apollo-graphql/src/signature.ts

@@ -43,7 +43,7 @@
 // the server no longer needs to parse the signature or run its own signature
 // algorithm on it, and the details of the signature algorithm are now up to the
 // reporting agent.
-
+import { createHash } from "crypto";
 import { DocumentNode } from "graphql";
 import {
   printWithReducedWhitespace,
@@ -66,3 +66,9 @@ export function defaultEngineReportingSignature(
     )
   );
 }
+
+export function hashForOperationSignature(operationSignature: string): string {
+  return createHash("sha256")
+    .update(operationSignature)
+    .digest("hex");
+}

packages/apollo/src/utils/getOperationManifestFromProject.ts

@@ -1,6 +1,8 @@
-import { createHash } from "crypto";
-import { defaultEngineReportingSignature } from "apollo-graphql";
 import { GraphQLClientProject } from "apollo-language-server";
+import {
+  defaultEngineReportingSignature,
+  hashForOperationSignature
+} from "apollo-graphql";
 
 export interface ManifestEntry {
   signature: string;
@@ -19,7 +21,7 @@ export function getOperationManifestFromProject(
     const printed = defaultEngineReportingSignature(operationAST, "");
 
     return {
-      signature: manifestOperationHash(printed),
+      signature: hashForOperationSignature(printed),
       document: printed,
       metadata: {
         engineSignature: printed
@@ -29,9 +31,3 @@ export function getOperationManifestFromProject(
 
   return manifest;
 }
-
-function manifestOperationHash(str: string): string {
-  return createHash("sha256")
-    .update(str)
-    .digest("hex");
-}