[java] Request body's of multipart/form-data requests are ignored by at least all Java generators

[lion7]

In the OpenAPI specification 3.0 an example of a multipart/form-data request body can be found (source):

requestBody:
  content:
    multipart/form-data:
      schema:
        type: object
        properties:
          id:
            type: string
            format: uuid
          address:
            # default Content-Type for objects is `application/json`
            type: object
            properties: {}
          profileImage:
            # default Content-Type for string/binary is `application/octet-stream`
            type: string
            format: binary
          children:
            # default Content-Type for arrays is based on the `inner` type (text/plain here)
            type: array
            items:
              type: string
          addresses:
            # default Content-Type for arrays is based on the `inner` type (object shown, so `application/json` in this example)
            type: array
            items:
              type: '#/components/schemas/Address'

The swagger-parser used by the generators parses this example different from other blocks; the schema is always a schema that refers to another schema, either an 'anonymous' schema or 1 that is defined in the components section, The current implementation of DefaultCodegenConfig does not follow this reference and hence all properties defined are ignored during code generation.