Option to preserve details disclosure element open attribute

[tatut]

It would be helpful to have an option to preserve the open attribute of a details element.
Many cases where a backend doesn't know (or care) if the element is open, but if it isn't preserved the details will close on re-render.

<details>
  <summary>Open to see my details</summary>
  <ul>
    <li>foo</li>
    <li>bar</li>
    <li>...</li>
  </ul>
</details>

Should this be a new option (like openness in modals/disclosure elements) or be done with the existing callbacks?

[tatut]

beforeAttributeUpdated: (e, n, v) => {
             if(e.tagName === 'DETAILS' && n === 'open')
                  return false;
                return true;
            }

way to implement with existing callback config

[joeldrapper]

Yeah, I agree this would be useful.

We should also test what happens with things like open dialogs and popovers. Ideally their state would be preserved too.