[BUG] graphql-schema and graphql-nodejs-express-server generate totally different graphql files

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Example API from graphql-schema: https://github.com/OpenAPITools/openapi-generator/blob/master/samples/config/petstore/graphql-schema/petstore/api/pet_api.graphql

Example API from graphql-nodejs-express-server: https://github.com/OpenAPITools/openapi-generator/blob/master/samples/server/petstore/graphql-nodejs-express-server/petstore/api/pet_api.graphql

There are several problems of the generated result when using graphql-schema, graphql-nodejs-express-server generates the correct result:

• Not type mutation, but type Mutation
• @return [null] is invalid
• # @param Pet is invalid, input and type should be seperated clearly

openapi-generator version

5.1.1

OpenAPI declaration file content or url

Provided before.

Suggest a fix

• I think the graphql-file generation logic of graphql-nodejs-express-server can be just migrated to graphql-schema
• Or graphql-schema can be just deprecated, then let graphql-nodejs-express-server generate only graphql files, but not the js part

Compare the referenced pet_api.graphql files under samples/config/petstore/graphql-schema and samples/server/petstore/graphql-nodejs-express-server. Trace the graphql-schema and graphql-nodejs-express-server generator entry points and templates, then run the relevant generator tests or petstore sample generation. Done means graphql-schema produces valid GraphQL matching the working generator’s expected mutations, return types, and input/type separation.