[BUG] [typescript] 'allOf' Inheritance causes enums to not be generated

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• 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?
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Description

When using allOf, an enum defined in the child object is not generated.

openapi-generator version

Discovered with 5.0.0, validated against master

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  description: example
  version: 0.0.0
  title: example
servers:
  - url: /
paths:
  /foo:
    get:
      tags:
        - foo
      summary: Lists all foos
      operationId: listFoos
      responses:
        '200':
          $ref: '#/components/responses/FooArrayResponse'
components:
  schemas:
    Foo:
      type: object
      title: A metasyntactic object
      allOf:
        - $ref: '#/components/schemas/Base'
      required:
      - mode
      properties:
        mode:
          type: string
          enum:
            - cloud
            - native

    Base:
      type: object
      title: Base class
      required:
        - id
      properties:
        id:
          description: Unique identifier
          format: uuid
          type: string

  responses:
    FooArrayResponse:
      description: Response containing multiple foos
      content:
        '*/*':
          schema:
            type: array
            items:
              $ref: '#/components/schemas/Foo'

Resultant foo.ts:

import { RequestFile } from './models';
import { Base } from './base';

export class Foo {
    'mode': Foo.ModeEnum;
    /**
    * Unique identifier
    */
    'id': string;

    static discriminator: string | undefined = undefined;

    static attributeTypeMap: Array<{name: string, baseName: string, type: string}> = [
        {
            "name": "mode",
            "baseName": "mode",
            "type": "Foo.ModeEnum"
        },
        {
            "name": "id",
            "baseName": "id",
            "type": "string"
        }    ];

    static getAttributeTypeMap() {
        return Foo.attributeTypeMap;
    }
}

Expected foo.ts:

import { RequestFile } from './models';
import { Base } from './base';

export class Foo {
    'mode': Foo.ModeEnum;
    /**
    * Unique identifier
    */
    'id': string;

    static discriminator: string | undefined = undefined;

    static attributeTypeMap: Array<{name: string, baseName: string, type: string}> = [
        {
            "name": "mode",
            "baseName": "mode",
            "type": "Foo.ModeEnum"
        },
        {
            "name": "id",
            "baseName": "id",
            "type": "string"
        }    ];

    static getAttributeTypeMap() {
        return Foo.attributeTypeMap;
    }
}

export namespace Foo {
    export enum ModeEnum {
        Cloud = <any> 'cloud',
        Native = <any> 'native'
    }
}

Steps to reproduce

java -jar openapi-generator-cli.jar generate -g typescript-node -i ./example.yml -o tmp/

Workarounds

If you define the enum as its own model, you can then $ref it with no issue:

components:
  schemas:
    ModeEnum:
      type: string
      enum:
        - cloud
        - native

...

      properties:
        mode:
          $ref: '#/components/schemas/ModeEnum'

Start with the typescript-node generator and the example.yml reproduction, then run the documented java -jar openapi-generator-cli.jar command. Compare the generated foo.ts with the expected output; the work is done when the Foo.ModeEnum namespace is generated for the child enum while the inherited fields remain present.