Add missing readFragment export in relay-runtime (#4931)

Summary:
this PR fixes #4926 by adding export `readFragment`

Pull Request resolved: #4931

Reviewed By: captbaritone

Differential Revision: D70646229

Pulled By: tyao1

fbshipit-source-id: c6cf80bf7eb12e4947baf3d6983fc7665dbf8e7f

Author: sairion

packages/relay-runtime/index.js

@@ -316,6 +316,7 @@ module.exports = {
   suspenseSentinel,
   isRequest: GraphQLTag.isRequest,
   readInlineData,
+  readFragment: ResolverFragments.readFragment,
 
   // Declarative mutation API
   MutationTypes: RelayDeclarativeMutationConfig.MutationTypes,