[BUG][typescript] `oneOf` + `allOf` breaks serialization

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

When using an API that uses a oneOf union containing several allOf elements, trying to send/receive data will fail with the error typeMap[type].getAttributeTypeMap is not a function. The underlying reason is that no discriminator value or mapping is generated for this value.

Prior to #19494 this worked fine, but as of 7.9.0 trying to run this schema will crash.

openapi-generator version

7.9.0, this is a regression.

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: fruity
  version: 0.0.1
paths:
  /:
    get:
      responses:
        "200":
          description: get a fruit
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Fruit"
components:
  schemas:
    Apple:
      title: Apple
      type: object
      properties:
        variety:
          type: string
          description: The type of apple
      required:
        - variety
    Banana:
      title: Banana
      type: object
      properties:
        ripeness:
          type: number
          description: How ripe the banana is from 0 to 1
    Fruit:
      title: Fruit
      oneOf:
        - type: object
          allOf:
            - type: object
              properties:
                type:
                  type: string
                  enum:
                    - apple
            - $ref: '#/components/schemas/Apple'
          required:
            - type
        - type: object
          allOf:
            - type: object
              properties:
                type:
                  type: string
                  enum:
                    - banana
            - $ref: '#/components/schemas/Banana'
          required:
            - type

Generation Details

Generated with v7.9.0.

Steps to reproduce

Generate the above yaml using the typescript generator, then try to use the API. It will fail with typeMap[type].getAttributeTypeMap is not a function

Related issues/PRs

Not as far as I could tell.

Suggest a fix

I don't have an exact fix in mind since I don't fully understand how this mapping logic is supposed to work.

Start by generating the supplied YAML with the TypeScript generator and reproduce the failure in the generated oneOf/allOf serialization path. Trace the typeMap handling and discriminator or mapping generation, then verify that requests and responses work for both Apple and Banana and add a regression test if the generator's existing test structure supports it.