Fix regression about popup close button modifying the URL

[IvanSanchez]

Fixes #8159

[Falke-Design]

I don't know if we should use DomEvent.stop(e) instead to prevent propagation.

Should we make a named function instead of a anonymus function? The developers would have access to the function for plugins / overwrites.

[IvanSanchez]

I don't know if we should use DomEvent.stop(e) to prevent propagation.

I'm not 100% sure. On one hand, and after giving this a bit of thought, I'm partial to go back to how things were before #7439, and use DomEvent.stop(ev). I cannot see how propagating the click event from the close button to the popup container can be useful.

On the other hand, I don't know if @johnd0e has a good use case about clicks on the popup close button being propagated. And, there's a disableClickPropagation() call being made on the popup container anyway, so there's no risk of propagating the event to the map container.

[mourner]

Let's do away with just preventDefault for the fix, and look into propagation separately, since it's not causing any apparent issues at the moment.

[IvanSanchez]

I think this is good "as is", then. No plugin author complained about the lack of a _onCloseButton method, and the preventDefault() should suffice.