[BUG][graphql-schema] doesn't support reuseble enum

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

graphql-schema generator doesn't support reusable enum

openapi-generator version

4.3.0

OpenAPI declaration file content or url

Resource:
      type: object
      properties:
        status:
            $ref: '#/components/schemas/ResourceStatus'
ResourceStatus:
      type: string
      enum:
        - a
        - b
        - c

Command line used for generation

npx openapi-generator generate -g graphql-schema -i example.yaml -o somedir

Steps to reproduce

Just run this command with schemas provided above, you will get an empty graphql file for this enum

# Paths for user service
# No description provided (generated by Openapi Generator https://github.com/openapitools/openapi-generator)
# The version of the OpenAPI document: 1.0.0
# Generated by OpenAPI Generator: https://openapi-generator.tech
#

type ResourceStatus {

}

Related issues/PRs

Suggest a fix

Start by running the listed npx openapi-generator command with the provided example.yaml and inspect the graphql-schema generator output for ResourceStatus. Compare the generated schema with the reusable enum values a, b, and c shown in the issue. Done means the generated GraphQL output represents those enum values instead of an empty type.