Add errors details to didEncounterErrors hook

[b1zzu]

In case an error is a SyntaxError or ValidationError this information is not passed to the didEncounterErrors hook. This missing piece of information is very important for logging plugins that may use it as a filter key to creating better metrics and monitoring alerts.

[apollo-cla]

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[glasser]

This seems like it would be a backwards-incompatible change so it probably isn't appropriate for AS3.

We've reworked our error handling code a lot on the version-4 branch. Among other things we don't actually end up using SyntaxError and ValidationError any more. It does look like we're still just passing the raw errors to didEncounterErrors, though. I am curious — is it possible that formatErrors would be a better place than didEncounterErrors to do your logging? Alternatively, perhaps we should apply something like this PR to version-4 where this backwards-incompatible change would be allowed.

@IvanGoncharov any thoughts?

[glasser]

(Or something like passing didEncounterErrors two arguments: the unformatted and formatted errors? (Or maybe the second argument would be an options object containing the formatted errors and maybe more stuff later))