Move stringifyForDisplay to utilities/common rather than /testing.

Fixing a regression introduced by #8508.

Importing from @apollo/client/testing in cache/inmemory/policies.ts made
Rollup display circular dependency warnings (which are often harmless
but also worth avoiding) and resulted in importing React-related code
even when using @apollo/client/core rather than @apollo/client, which is
a more serious problem.

src/__tests__/__snapshots__/exports.ts.snap

@@ -312,7 +312,6 @@ Array [
   "itAsync",
   "mockObservableLink",
   "mockSingleLink",
-  "stringifyForDisplay",
   "stripSymbols",
   "subscribeAndCount",
   "withErrorSpy",
@@ -377,6 +376,7 @@ Array [
   "resultKeyNameFromField",
   "shouldInclude",
   "storeKeyNameFromField",
+  "stringifyForDisplay",
   "valueToObjectRepresentation",
 ]
 `;

src/cache/inmemory/policies.ts

@@ -22,6 +22,7 @@ import {
   getStoreKeyName,
   canUseWeakMap,
   isNonNullObject,
+  stringifyForDisplay,
 } from '../../utilities';
 import {
   IdGetter,
@@ -52,7 +53,7 @@ import { WriteContext } from './writeToStore';
 // used by getStoreKeyName. This function is used when computing storeFieldName
 // strings (when no keyArgs has been configured for a field).
 import { canonicalStringify } from './object-canon';
-import { stringifyForDisplay } from '../../testing';
+
 getStoreKeyName.setStringify(canonicalStringify);
 
 export type TypePolicies = {

src/utilities/testing/stringifyForDisplay.ts → src/utilities/common/stringifyForDisplay.ts

@@ -1,4 +1,4 @@
-import { makeUniqueId } from "../common/makeUniqueId";
+import { makeUniqueId } from "./makeUniqueId";
 
 export function stringifyForDisplay(value: any): string {
   const undefId = makeUniqueId("stringifyForDisplay");

src/utilities/index.ts

@@ -94,5 +94,6 @@ export * from './common/errorHandling';
 export * from './common/canUse';
 export * from './common/compact';
 export * from './common/makeUniqueId';
+export * from './common/stringifyForDisplay';
 
 export * from './types/IsStrictlyAny';

src/utilities/testing/index.ts

@@ -14,4 +14,3 @@ export { stripSymbols } from './stripSymbols';
 export { default as subscribeAndCount } from './subscribeAndCount';
 export { itAsync } from './itAsync';
 export * from './withConsoleSpy';
-export * from './stringifyForDisplay';

src/utilities/testing/mocking/mockLink.ts

@@ -15,11 +15,8 @@ import {
   removeClientSetsFromDocument,
   removeConnectionDirectiveFromDocument,
   cloneDeep,
-} from '../../../utilities';
-
-import {
   stringifyForDisplay,
-} from '../../../testing';
+} from '../../../utilities';
 
 export type ResultFunction<T> = () => T;