Replace ObservableQueryFields with ObservableQuery in apollo-client

[skovy]

Intended outcome:

• react-apollo uses the types defined in apollo-client added in Improved type definitions for the observable query apollo-client#3140

Actual outcome:

• The types are defined twice, in both react-apollo and apollo-client 😱

How to reproduce the issue:

This is a basic example. With the update previousQueryResult should be typed as PersonQueryResult. See this apollo-client issue: apollographql/apollo-client#3391

const GET_PERSON = gql`
  {
    person {
      id
      name
    }
  }
`;

interface PersonQueryResult {
  person: {
    name: string;
  }
}

class PersonQuery extends Query<PersonQueryResult> {};

class MyComponent extends React.Component {
  render() {
    return <PersonQuery query={GET_PERSON}>
      {({ subscribeToMore }) => {
        subscribeToMore({
          document: GET_PERSON,
          updateQuery: (previousQueryResult) => {
            return previousQueryResult;
          }
        });

        return <div />;
      }}
    </PersonQuery>
  }
}

Relevant PRs:

• Improve subscribeToMore types
• Improved type definitions for the observable query
• Improve Query and graphql types. Strict type check with Typescript

[rosskevin]

PR welcome.

[hwillson]

This was addressed in #2281. Thanks!