[BUG] Problem with underscore (_) in form field names

[dJani97]

Describe the bug
When generating formData requests, the generator doesn't handle underscore (_) in form field names well.

To Reproduce
I have the following request in our API definition:

{
  "/register":{
    "post":{
      "consumes":[
        "application/x-www-form-urlencoded"
      ],
      "produces":[
        "application/json"
      ],
      "parameters":[
        {
          "name":"name",
          "in":"formData",
          "required":true,
          "type":"string"
        },
        {
          "name":"email",
          "in":"formData",
          "required":true,
          "type":"string"
        },
        {
          "name":"password",
          "in":"formData",
          "required":true,
          "type":"string"
        },
        {
          "name":"password_confirmation",
          "in":"formData",
          "required":true,
          "type":"string"
        }
      ],
      "responses": ...
    }
  }
}

When generating the client, the output is the following Dart code:

  ///@param name name of user
  ///@param email email of user
  ///@param password password of user
  ///@param password_confirmation password confirmation of user
  @Post(path: '/register', optionalBody: true)
  Future<chopper.Response<User>> registerPost(
      {@Field() required String? name,
      @Field() required String? email,
      @Field() required String? password,
      @Field() required String? passwordConfirmation});

As you can see, the field password_confirmation appears as camel case in the code. This does not get processed by the API and the request fails.

Expected behavior

The proper output should include the password_confirmation field as follows:

      @Field('password_confirmation') required String? passwordConfirmation});

Library version used:

swagger_dart_code_generator: ^2.2.2
json_annotation: ^4.3.0
chopper_generator: ^4.0.2