Fix error handling for observer.next

[cannoneyed]

When observer.next is called in queryListenerForObserver based on the results of a given query and itself throws an error, the error handling logic surrounding it automatically casts that error into an ApolloError, even though it didn't originate within apollo-client.

This is a big problem in react-apollo (see this issue). observer.next calls the method that forces a rerender, and when child components throw an error they bubble up and wind up being handled by the catch statement in queryListenerForObserver, which turns it into an ApolloError, effectively swallowing the error.

This PR rearranges the error handling logic in order to effectively capture errors that occur within apollo-client (such as mismatches in data being read from the store) and allows errors that occur outside of apollo-client (when thrown from within observer.next) to propagate correctly.

TODO:

• If this PR is a new feature, reference an issue where a consensus about the design was reached (not necessary for small changes)
• 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
• Add your name and email to the AUTHORS file (optional)
• If this was a change that affects the external API, update the docs and post a link to the PR in the discussion

[apollo-cla]

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[helfer]

@cannoneyed Thanks for this great PR! This simple change should make debugging a lot easier.

Looking at the code, it is possible that transformResult throws an error which no longer gets caught, but I think that's okay since transformResult is either user-provided, or doesn't do anything.