Add Inheritance with use of anyOf and no discriminator

[arvindkrishnakumar-okta]

Fixes #9756

This PR contains changes to add missing Inheritance hierarchy when anyOf is used without discriminator in Open API Spec.

Given the below spec for e.g.:

openapi: 3.0.2
info:
  title: OAI Specification example for Polymorphism
  version: 1.0.0
paths:
  /pet:
    get:
      responses:
        '200':
          description: desc
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Pet'
  /cat:
    get:
      responses:
        '200':
          description: desc
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Cat'
components:
  schemas:
    Pet:
      type: object
      properties:
        prop-x:
          type: boolean
    Cat:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            prop-y:
              type: boolean

Expected:

DefaultCodegen codegen = new DefaultCodegen();
codegen.setLegacyDiscriminatorBehavior(false);
codegen.setOpenAPI(openAPI);

Schema catSchema = openAPI.getComponents().getSchemas().get("Cat");
CodegenModel catModel = codegen.fromModel("Cat", catSchema);

assertEquals(catModel.getParent(), "Pet"); 

Actual:

catModel.getParent() is NULL

This PR intends to fix the above issue.

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