#1268: Error when store a big data to cache

[rigoucr]

ISSUE: #1268 Error when store a big data to cache.

This PR Fixes the schema cache issue when your schema reach out certain size.

• Issue description: when your schema reach certain size the Parsed schema object ( DocumentNode) becomes unmanageable by the unserialize function, leading to not loading the right cached schema data .

  How to do a basic a test:

• [ ] Apply this patch https://github.com/drupal-graphql/graphql/pull/1272.patch
• [ ] clear drupals cache ( drush cr )
• [ ] load the graphql explorer page admin/config/graphql/servers/manage/[SERVER-ID]/explorer
• [ ] It should load without any issues
• [ ] Now reload the explorer page, it should keep working as expected.

[klausi]

Should be fixed by #1364, so I think we don't need this. Please test!