ENH: [Client generator] Add Map<String,?> option for header() queryParam() and formParam()

[rbygrave]

With this we can use Map<String, ?> parameter types for @QueryParam, @Header and @FormParam and these are then passed as a map to the set multiple query parameters, headers, or form parameters.

Example

  @Get("{uid}/withParams")
  HttpResponse<String> withParams(long uid, @QueryParam Map<String, ?> params);

Generates the code below ...

  // GET {uid}/withParams
  @Override
  public HttpResponse<String> withParams(long uid, Map<String,?> params) {
    return clientContext.request()
      .path("moo").path(uid).path("withParams")
      .queryParam(params)
      .GET()
      .asString();
  }

Note that the .queryParam(params) sets the map of query parameters to the request.