feat: add details to the "close" event

The close event will now include additional details to help debugging
if anything has gone wrong.

Example when a payload is over the maxHttpBufferSize value in HTTP
long-polling mode:

```js
socket.on("close", (reason, details) => {
  console.log(reason); // "transport error"

  // in that case, details is an error object
  console.log(details.message); "xhr post error"
  console.log(details.description); // 413 (the HTTP status of the response)

  // details.context refers to the XMLHttpRequest object
  console.log(details.context.status); // 413
  console.log(details.context.responseText); // ""
});
```

Note: the error object was already included before this commit and is
kept for backward compatibility

Example when a payload is over the maxHttpBufferSize value with
WebSockets:

```js
socket.on("close", (reason, details) => {
  console.log(reason); // "transport close"

  // in that case, details is a plain object
  console.log(details.description); // "websocket connection closed"

  // details.context is a CloseEvent object
  console.log(details.context.code); // 1009 (which means "Message Too Big")
  console.log(details.context.reason); // ""
});
```

Example within a cluster without sticky sessions:

```js
socket.on("close", (reason, details) => {
  console.log(details.context.status); // 400
  console.log(details.context.responseText); // '{"code":1,"message":"Session ID unknown"}'
});
```

Note: we could also print some warnings in development for the "usual"
errors:

- CORS error
- HTTP 400 with multiple nodes
- HTTP 413 with maxHttpBufferSize

but that would require an additional step when going to production
(i.e. setting NODE_ENV variable to "production"). This is open to
discussion!

Related:

- https://github.com/socketio/socket.io/issues/3946
- https://github.com/socketio/socket.io/issues/1979
- https://github.com/socketio/socket.io-client/issues/1518