Content-type "multipart/form-data" generates actions with individual parameters, not single object like "application/json"

Description

content-type multipart/form-data and application/json generate different action signatures.

Swagger-codegen version

Used online version at https://editor.swagger.io/

Swagger declaration file content or url

The following example generates a DefaultApi class that takes individual parameters:

openapi: 3.0.3
info:
    title: 'Test API'
    description: 'Test v3 API'
    termsOfService: 'https://www.example.com/terms'
    contact:
        email: apisupport@example.com
    license:
        name: MIT
        url: 'https://opensource.org/licenses/MIT'
    version: 3.0.0
servers:
    -
        url: 'https://api.example.com/v3'
paths:
    /pets:
        patch:
            requestBody:
                content:
                    multipart/form-data:
                        schema:
                            $ref: '#/components/schemas/Dog'
            responses:
                '200':
                    description: Updated
components:
    schemas:
        Dog:
            type: object
            properties:
                bark:
                    type: boolean
                breed:
                    type: string
                    enum: [Dingo, Husky, Retriever, Shepherd]

This is the generated DefaultApi::petsPatch() method:

    /**
     * Operation petsPatch
     *
     * @param  bool $bark bark (optional)
     * @param  string $breed breed (optional)
     *
     * @throws \Swagger\Client\ApiException on non-2xx response
     * @throws \InvalidArgumentException
     * @return void
     */
    public function petsPatch($bark = null, $breed = null)
    {
        $this->petsPatchWithHttpInfo($bark, $breed);
    }

However, changing multipart/form-data to application/json produces the following DefaultApi::petsPatch() method:

    /**
     * Operation petsPatch
     *
     * @param  \Swagger\Client\Model\Dog $body body (optional)
     *
     * @throws \Swagger\Client\ApiException on non-2xx response
     * @throws \InvalidArgumentException
     * @return void
     */
    public function petsPatch($body = null)
    {
        $this->petsPatchWithHttpInfo($body);
    }

Note that both examples generate a \Swagger\Client\Model\Dog class, but only the application/json example uses this class.

Suggest a fix/enhancement

A flag should be accepted by swagger-codegen that forces the use of created object in relevant action methods.

Reproduce the issue in the online editor using the supplied OpenAPI 3.0.3 document and compare the generated PHP DefaultApi::petsPatch() signatures for multipart/form-data and application/json. Trace the requestBody handling and Mustache-generated PHP output; done means multipart/form-data uses the generated Dog model consistently, with the relevant behavior covered by a regression check.