WIP: Fix `@interfaceObject` + `__typename` / key bug

[trevor-scheer]

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Just a repro for now. As it stands currently, the query plan in the snapshot is correct but the test fails. The entire ... on T1 is unexpectedly missing.

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[michael-watson]

Just wanted to add a confirmed workaround for this problem. Any field on the interface could be defined at the root of that interface and not duplicated in the fragments.

From the test in this repo:

query {
    itfObj {
      __typename
      ... on T1 {
        __typename
        id
      }
      ... on T2 {
        # Uncomment id to break operation
        # id
        __typename
      }
    }
  }

Could be this to fix it and generate the appropriate plan:

query {
    itfObj {
        id
      __typename
      ... on T1 {
        __typename
      }
      ... on T2 {
        __typename
      }
    }
  }