[RFC]: add `@stdlib/iter/cartesian-square`

### Description

This RFC proposes adding the package `@stdlib/iter/cartesian-square`.

This package would be the iterator equivalent of [`@stdlib/array/cartesian-square`](https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/cartesian-square).

```javascript
function iterCartesianSquare( x ) { ... }
```

where `x` is an input array-like object.

Package: `@stdlib/iter/cartesian-square`
Alias: `iterCartesianSquare`

### Related Issues

No.

### Questions

No.

### Other

No.

### Checklist

- [X] I have read and understood the [Code of Conduct](https://github.com/stdlib-js/stdlib/blob/develop/CODE_OF_CONDUCT.md).
- [X] Searched for existing issues and pull requests.
- [X] The issue name begins with `RFC:`.