WIP: Array parameters in URL (#3529)

[Pankraty]

Hi!

We faced with the issue described in #3529 when the TypeScript client ignores the style attribute of a parameter passed in URL. For example, we have a schema defining input argument like this:

  "parameters": [
  {
    "name": "eventTypes",
    "in": "query",
    "style": "form",
    "explode": false,
    "schema": {
        "type": "array",
        "items": {
        "$ref": "#/components/schemas/EventTypes"
        },
        "nullable": true
    }
  },
  ...

and Swagger UI does build the URL as xxx?eventTypes=EventA,EventB which is exactly what we are expecting. But NSwag - both TypeScript and C# version - serializes parameters differently: xxx?eventTypes=EventA&eventTypes=EventB and so on.

I would like to contribute to the library and make necessary changes, and here is the first draft. It is not a completed work, for example, there should be additional checks for IsDateOrDateTimeArray. Additionally, I am going to make similar changes to C# generators and write tests. But before I spent too much time on this I wanted to get a confirmation from you that this is the right way to go.

With these changes, I was able to produce such code for my TypeScript client:

1. When style=matrix

    republishEvents(eventTypes: EventTypes[] | null | undefined): Promise<number> {
        let url_ = this.baseUrl + "/api/v1/data/republishevents?";
        if (eventTypes !== undefined && eventTypes !== null)
        {
            eventTypes.forEach(item => { url_ += "eventTypes=" + encodeURIComponent("" + item) + ";"; });
            url_ = url_.replace(/;$/, "");
        }
        url_ = url_.replace(/[?&]$/, "");

2. When style=form

    republishEvents(eventTypes: EventTypes[] | null | undefined): Promise<number> {
        let url_ = this.baseUrl + "/api/v1/data/republishevents?";
        if (eventTypes !== undefined && eventTypes !== null)
            if (eventTypes.length)
            {
                url_ += "eventTypes=";
                eventTypes.forEach(item => { url_ += encodeURIComponent("" + item) + ","; });
                url_ = url_.replace(/,$/, "");
            }
        url_ = url_.replace(/[?&]$/, "");

Maybe not the best JS code I ever saw, but it seems to do what we need.

Looking forward to hearing back from you, @RicoSuter!