feat: ScalarFieldToObjectFieldRewriter

This PR adds a new rewriter type called ScalarFieldToObjectFieldRewriter. This rewriter allows rewriting a field that's a scalar, like title: 'blah', to an object with a single nested scalar, like { title: { text: 'blah' } }.

For example, this would allow transitioning from a schema like:

type Article {
  title: String!
  ...
}

type ArticleTitle {
  text: String!
  localizedText: string
}

type Article {
  title: ArticleTitle!
 ...
}

The rewriter to do this would look like:

new ScalarFieldToObjectFieldRewriter({
    fieldName: 'title',
    objectFieldName: 'text'
})

Then, when an old query arrives requesting:

query {
  article(id: 123) {
    title
  }
}

this will be rewritten to

query {
  article(id: 123) {
    title {
      text
    }
  }
}

graphql-query-rewriter / core

feat: ScalarFieldToObjectFieldRewriter #7