This comes up when filtering on a nested field in a related collection. For example, where there is a relation from comments to movie:

query {
  comments(where: {movie: {imdb: {rating: {_eq: 9.2}}}}) {
    text
    movie {
      title
      year
    }
  }
}

In this example no records are returned because imdb.rating is not in scope when during filtering where that where predicate is applied.

We already have logic in place to include columns in joins if they are needed for an expression. But that logic did not account for nested fields. This PR updates the query planner to recursively include nested fields as needed if they are used in expressions.