[BUG][CSHARP] DeepObject query params are not sent in the Api when additional properties are enable

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Currently there is support of deepObjects on query params which produces parameters with square brackets.
Example: Query param named fields can produce /endpoint?fields["key_1"]=value_1&fields["key_2"]=value2

When the query param is deepobject and additional properties is allowed, the generated code creates APIs that does nothing to the query param.

 - name: fields
          in: query
          description: Holds types of fields and its values
          style: deepObject
          explode: true
          schema:
            type: object
            additionalProperties:
              type: string
            description: Dictionary that holds the optional query filters of a request called fields. This dictionary is case insensitive.

Generated API

localVarRequestOptions.PathParameters.Add("userId", Sdk.Client.ClientUtils.ParameterToString(userId)); // path parameter
            if (fields != null)
            {
            }

Expected behavior

When the deepobject query-param with additional properties is found, the API generated code should be

if (fields != null)
{
    localVarRequestOptions.QueryParameters.Add(Sdk.Simple.Client.ClientUtils.ParameterToMultiMap("deepObject", "fields", fields));
}

Note: Support for deepObject is already there but when object only support "additional objects" it does nothing.

openapi-generator version

v7.7.0

OpenAPI declaration file content or url

Use the following swagger to generate the API code in csharp

openapi: 3.0.1
info:
  title: Testing single
  version: 0.0.1
paths:
  /single/session/{userId}:
    get:
      summary: Single endpoint session
      parameters:
        - name: fields
          in: query
          description: Holds types of fields and its values
          style: deepObject
          explode: true
          schema:
            type: object
            additionalProperties:
              type: string
            description: Dictionary that holds the optional query filters of a request called fields. This dictionary is case insensitive.
        - name: userId
          in: path
          description: The identity of the user.
          required: true
          schema:
            type: string

Complete swagger in: https://gist.github.com/alfredo-accuris/65e5961ff763e00bc7dd6718b192b8a9

Generation Details

docker run --rm openapitools/openapi-generator-cli:v7.7.0 generate -i ./deepobject-swagger.json --package-name Simple -g csharp -o ./Sdk/Simple --additional-properties targetFramework=net8.0

Steps to reproduce

Execute the cli with the specific swagger.

Related issues/PRs

Suggest a fix

Going through the code I can see on org.openapitools.codegen.DefaultCodegen that has a property loadDeepObjectIntoItems=true that always tries to load specify keys for deepobjects but if the variable is set to false, then the generated code works as expected generating:

if (fields != null)
{
    localVarRequestOptions.QueryParameters.Add(Sdk.Simple.Client.ClientUtils.ParameterToMultiMap("deepObject", "fields", fields));
}

I suggest make the loadDeepObjectIntoItems configurable to support both options.

Start with org.openapitools.codegen.DefaultCodegen and the loadDeepObjectIntoItems property, then reproduce the issue using the supplied OpenAPI YAML and C# generation command. Compare generated handling of a deepObject query parameter with additionalProperties against the expected QueryParameters call, and verify the behavior after the configuration is addressed.