Feat/stiched errors extensions

[carmelid]

By using the GraphQLError constructor directly we are able to pass extensions through, as opposed to when using locatedError which does not produce a GraphQLError with extensions. This means that remote custom extensions can be passed through and not get lost along the way.

• If this PR is a new feature, reference an issue where a consensus about the design was reached (not necessary for small changes) (small change IMO)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change. Include a description of your change, link to PR (always) and issue (if applicable). Add your CHANGELOG entry under vNEXT. Do not create a new version number for your change yourself.

[carmelid]

I also took the liberty to fix some of the tests that had been breaking. @abernix @trevorblades @hwillson

[yaacovCR]

Closed in favor of #1307