Support using a @tag value defined inside a @fold

[obi1kenobi]

The systematic solution for this requires support for exporting @tag values across @fold boundaries, to allow a query structure like:

{
  baseline {
    item {
      importable_path @fold {
        name @tag(name: "paths")
      }
    }    
  }
  current {
    item {
      importable_path @fold @transform(op: "count") @filter(op: ">", value: ["$zero"]) {
        name @filter(op: "one_of", value: ["$paths"])
      }
    }
  }
}

In this query, the tagged paths value at the point of use is of type [String!]! because it is folded over before being used. Inside its own @fold scope, the tagged value is of type String! as normal.

Originally posted by @obi1kenobi in obi1kenobi/cargo-semver-checks#277 (comment)