Add test to emit custom event

[Grafikart]

I'm currently encountering a problem with svelte and I think it could be interesting to know if other framework has this caveat.

The goal of the test is to see if a custom element produced by a framework can emit a CustomEvent.

<my-element></my-element>
<script>
document.querySelector('my-element').addEventListener('myevent', function (e) {

});
</script>

The sentence would be

• The library/framework should be able to dispatch DOM events from a custom element. These DOM events could be listened from the outside.

[rictic]

This is a good test to add if we add a suite for the ability to produce a web component with each library