Add support for multiple fragments merging in ReplaceFieldWithFragment

[maticzav]

Hello 👋,

This is a feature request for supporting automatical merging of multiple fragments with same field and typeCondition.

Transform

const transforms = [
  new ReplaceFieldWithFragment(subSchema, [
    {
      field: `fullname`,
      fragment: `fragment UserName on User { name }`,
    },
    {
      field: `fullname`,
      fragment: `fragment UserSurname on User { surname }`,
    },
  ]),
]

query {
  userById(id: "ID") {
    fullname
  }
}

Expected behaviour

query {
  someQuery(id: "ID") {
    ...on User {
      name
      surname
    }
  }
}

Actual Behaviour

query {
  someQuery(id: "ID") {
    ...on User {
      surname
    }
  }
}

This happens due to default overwriting of the fragments instead of collecting them.

Use cases

• GraphQL Binding - this would enable overlapping fragmentReplacements which have to be handled manually at the moment.
• GraphQL Middleware - this would enable fragments support in graphql-middleware where we need support for a list of different fragmentsReplacements extracted from different middleware.

[yaacovCR]

Closed by #895