[BUG][Angular] Query parameters with additionalProperties not serialized

Description

Having the following spec:

'/v1/job':
    get:
      parameters:
      ...
        - name: sort
          in: query
          required: false
          style: form
          explode: false
          schema:
            type: object
            additionalProperties:
              type: string
              enum:
                - asc
                - desc

The TS is correctly generated:

    getJobs(jobType: string, search?: string, limit?: number, page?: number, sort?: {
        [key: string]: 'asc' | 'desc';
    }, observe?: 'body', reportProgress?: boolean): Observable<Page>;

But the item is not serialized, instead I get a query like this: host/job?sort=[object Object]

Command line used for generation

/bin/docker run [...] openapitools/openapi-generator-cli generate -i source.yaml -g typescript-angular -o /data/sdk/angular --additional-properties=npmName=@api,withInterfaces=true,ngVersion=7.0.0

Suggest a fix/enhancement

Dictionary types should be serialized according to https://swagger.io/docs/specification/serialization/

Reproduce the issue with the supplied OpenAPI specification and the typescript-angular generator command. Start by tracing how the generated getJobs method serializes query parameters, focusing on object values with additionalProperties. Done means the sort dictionary is serialized according to the referenced OpenAPI rules instead of becoming [object Object].