[BUG] csharp-netcore different handling of deepObject GET parameters between async and sync methods

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

The example below uses style:deepObject in components/parameters/GeoPosition. The generated csharp-netcore method for sync calls is handling the position parameter as follows:

            if (position != null)
            {
                if (position.Lat != null)
                {
                    localVarRequestOptions.QueryParameters.Add(Org.OpenAPITools.Client.ClientUtils.ParameterToMultiMap("", "position[lat]", position.Lat));
                }
                if (position.Lon != null)
                {
                    localVarRequestOptions.QueryParameters.Add(Org.OpenAPITools.Client.ClientUtils.ParameterToMultiMap("", "position[lon]", position.Lon));
                }
            }

But the async method is doing:

            if (position != null)
            {
                localVarRequestOptions.QueryParameters.Add(Org.OpenAPITools.Client.ClientUtils.ParameterToMultiMap("", "position", position));
            }

So the string representation of the generated GeoPosition class get added to the parameter when using async methods.

openapi-generator version

cli-5.2.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: My Api
  version: 1.0.0
paths:
  /registration:
    get:
      operationId: getRegistration
      parameters:
        - $ref: '#/components/parameters/GeoPosition'
      responses:
        '200':
          description: successful registration
components:
  parameters:
    GeoPosition:
      name: position
      in: query
      required: false
      style: deepObject
      schema:
        $ref: '#/components/schemas/GeoPosition'
  schemas:
    GeoPosition:
      type: object
      nullable: true
      properties:
        lat:
          type: number
        lon:
          type: number

Generation Details

Steps to reproduce

java -jar openapi-generator-cli-5.2.0.jar generate -i myapi.yaml -g csharp-netcore

have a look into DefaultApi.cs and compare GetRegistrationWithHttpInfoAsync vs. GetRegistrationWithHttpInfo

Related issues/PRs

Suggest a fix

async methods should have the same code generated as the sync methods. To clarify: the sync method is ok. The async method is faulty.

Generate the provided OpenAPI example with openapi-generator-cli 5.2.0 using the csharp-netcore generator, then inspect DefaultApi.cs. Compare GetRegistrationWithHttpInfoAsync with GetRegistrationWithHttpInfo, focusing on how the deepObject position parameter is added. Done means both methods generate equivalent position[lat] and position[lon] query handling.