[BUG] OpenAPI Normalizer - Unnecessary allOf wrapping for oneOf/anyOf items with discriminator labels

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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

The OpenAPINormalizer wraps oneOf and anyOf items into allOf compositions when they have discriminator labels (e.g., title field).

openapi-generator version

OpenAPI declaration file content or url

Pet:
  oneOf:
    - title: dog  
      description: "A dog pet"
      $ref: '#/components/schemas/Dog'
    - title: cat  
      description: "A cat pet"
      $ref: '#/components/schemas/Cat'
    - title: bird  
      description: "A bird pet"
      $ref: '#/components/schemas/Bird'

Actual:

Pet:
  oneOf:
    - allOf:  
        - $ref: '#/components/schemas/Dog'
      title: dog
      description: "A dog pet"
    - allOf:  
        - $ref: '#/components/schemas/Cat'
      title: cat
      description: "A cat pet"
    - allOf:  
        - $ref: '#/components/schemas/Bird'
      title: bird
      description: "A bird pet"
  discriminator:
    propertyName: petType

expected. For oneOf/anyOf discriminator labels, we should leave them unchanged.

Pet:
  oneOf:
    - title: dog 
      description: "A dog pet"
      $ref: '#/components/schemas/Dog'
    - title: cat  
      description: "A cat pet"
      $ref: '#/components/schemas/Cat'
    - title: bird  
      description: "A bird pet"
      $ref: '#/components/schemas/Bird'
  discriminator:
    propertyName: petType

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Implement context-aware normalization. skip normalization for oneOf/anyOf items, but keep normalizing regular properties.

Start at the OpenAPINormalizer entry point and reproduce the issue with the supplied Pet schema using oneOf and discriminator labels. Trace how oneOf/anyOf items are normalized, then verify that these labeled items remain unchanged while regular properties continue to be normalized.