[BUG] [CORE] Don't have the inline model resolver extract composed schemas

[spacether]

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

Per our conversation in #4906
When parsing a composed schema, the inline model resolver should not extract composed schemas per the Openapi spec:

Specifically, the spec at https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.2.md#discriminator-object says:

When using the discriminator, inline schemas will not be considered.

openapi-generator version

master branch

OpenAPI declaration file content or url

    FruitInlineDisc:
      oneOf:
        - type: object
          required:
            - seeds
            - fruitType
          properties:
            seeds:
              type: integer
            fruitType:
              type: string
        - type: object
          required:
            - length
            - fruitType
          properties:
            length:
              type: integer
            fruitType:
              type: string
      discriminator:
        propertyName: fruitType

Command line used for generation

use the python generator with this spec

Steps to reproduce

Debug the models and you will see that new models are created from the composed inline schemas. They should not be extracted.

Related issues/PRs

#4906

Suggest a fix

Don't extract the inline schemas when a composed schema has a discriminator

[spacether]

Closing this because there are more important tickets to work on