Enable saving the response to a file after running the request handler

By default the response is saved in a file `{{$historyFolder}}/{{ISO 8601 date-time}}.{{responseStatus}}.json`

Currently I am able to override it like this:

```
###
GET http://host/request

>>! {{$historyFolder}}/my-request.v{{apiVersion}}.json
```

Where apiVersion comes from the selected environment. However, I am also interested in putting the response's status code in the filename (in the same way as the default), but I don't seem to be able to make it work like below, because the response is saved to a file _before_ the response handler script is ran. This means `responseStatus` contains either nothing, or the previous request's response status.

```
###
GET http://host/request

> {%
client.global.set("responseStatus", response.status.toString());
%}

>>! {{$historyFolder}}/my-request.v{{apiVersion}}.{{responseStatus}}.json
```

**Other thoughts:**

- An alternative solution for this specific use case may be to add a `$responseStatus` variable (next to `$timestamp`, `$randomInt`, etc.) although that variable's value would depend on a changing context, which doesn't seem to be the intention of those existing variables. It seems to me the original proposal would bring more flexibility.
- The execution order of saving/handling could even be made dependent on the order of the commands as they appear after the request in the `.http`-file. So by placing the `> file.js` or `> {% /* ... */ %}` response handler _after_ the saving instruction (if both are specified), the current/old behavior can still be attained.

Start by tracing the response-saving step and response-handler execution order described in the issue. Compare post-handler filename evaluation with the proposed command-order alternative; done means the specification defines a consistent order and allows the response status to be used when naming the saved file.

Written by the indexing model from the issue text.