Heuristic fragment matcher

[eric-burel]

When upvoting in example-forum:

You are using the simple (heuristic) fragment matcher, but your queries contain union or interface types. Apollo Client will not be able to accurately map fragments. To make this error go away, use the IntrospectionFragmentMatcher as described in the docs: https://www.apollographql.com/docs/react/advanced/fragments.html#fragment-matcher

[eric-burel]

@SachaG I see a commit related to this in the apiSchema improvements, was it meant to fix this issue?