[openable] Under what conditions should openable JS methods throw?

[lukewarlow]

Should JS methods throw under various circumstances:

When the element isn’t connected to the document?
When the element’s node document isn’t fully active?
When the element is open as a non-modal dialog?
When the element is open as a modal dialog?
When the element is open as a popover?
When the element is a fullscreen element?

Popover has a variety of restrictions such as this so we should decide the same for openables.

[github-actions]

There hasn't been any discussion on this issue for a while, so we're marking it as stale. If you choose to kick off the discussion again, we'll remove the 'stale' label.