Accordion item stay opened when another accordion item is opened

Grimreaper → credited pdureau → .

After discussion with @maboy and @pdureau.

Needs to do that in JS because when preprocessing accordion pattern we get the render array of a content entity (paragraph) so the existing preprocess is not able to inject attributes.
Remove heading level settings on accordion, no way to set it on accordion item.

Automatically closed - issue fixed for 2 weeks with no activity.