[BUG] Order of parameter in form data is not garantee according the description file

Description

http://www.w3.org/TR/html4/interact/forms.html#h-17.13.4 define that form data must be send in the order of the declaration

"The parts are sent to the processing agent in the same order the corresponding controls appear in the document stream. "

openapi-generator version

bug exist in all version. I tries maven plugin 4.3.1 and 5.0

OpenAPI declaration file content or url

"multipart/form-data": {
"schema": {
"type": "object",
"title": "CreatedMessage",
"required": [
"subject",
"comment",
],
"properties": {
"subject": {
"type": "string",
"example": "Very important files"
},
"comment": {
"type": "string",
"example": "Please review this document ASAP"
},

Generation Details

The main problem is related to sendXCall where X is the method. There is in generated code
Map<String, String> localVarCookieParams = new HashMap<String, String>();
Map<String, Object> localVarFormParams = new HashMap<String, Object>();

Steps to reproduce

generate an openapi file with formdata

Related issues/PRs

Suggest a fix

As localVarFormParams is an HashMap, order of retrieving according to the order of insertion is not garantee.
My correction was to create localVarFormParams as a LinkedHashMap

Start at the generated sendXCall method and inspect where localVarFormParams is initialized and iterated. Reproduce a multipart/form-data client from the provided declaration, then verify that subject and comment are sent in declaration order across the relevant generated client output.