Improve the Return Type Validation in GraphQL Interceptors

[DimuthuMadushan]

Description:
When returning a value that includes a map from a GraphQL interceptor, It's not validated correctly.
Consider the following GraphQL service:

import ballerina/graphql;

public type Languages record {|
    map<string> name;
|};

readonly service class InterceptMap {
    *graphql:Interceptor;

    isolated remote function execute(graphql:Context context, graphql:Field 'field) returns anydata|error {
        Languages ls = {
            name: {
                backend: "PHP",
                frontend: "Flutter",
                data: "Ballerina",
                native: "java"
            }
        };
        var result = context.resolve('field);
        if 'field.getName() == "languages"{
            return ls;
        }
        return result;
    }
}

@graphql:ServiceConfig {
    interceptors: [new InterceptMap()]
}
service /gql_map on new graphql:Listener(9000) {
    private final Languages languages;

    function init() {
        self.languages = {
            name: {
                backend: "Ballerina",
                frontend: "JavaScript",
                data: "Python",
                native: "C++"
            }
        };
    }

    isolated resource function get languages() returns Languages {
        return self.languages;
    }
}

If we query the service as follows:

query {
  languages {
    name(key:"backend")
  }
}

It returns the following response.

{
  "data": {
    "languages": {
      "name": {}
    }
  }
}

But the actual response should be as follows:

{
  "data": {
    "languages": {
      "name": "PHP"
    }
  }
}