Append dropped items to the list handling the drop event - #13145

Append the new list item to event.currentTarget in the drag-and-drop example.

The handler is attached to the ol. When a drop targets an existing li and bubbles to the list, event.target is that li; appending there nests the new item inside it. currentTarget keeps the destination as the list.

Spec: https://html.spec.whatwg.org/multipage/dnd.html#event-drag

• At least two implementers are interested (and none opposed):
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• Tests are written and can be reviewed and commented upon at:
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• Implementation bugs are filed:
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  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): …
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• Corresponding HTML AAM & ARIA in HTML issues & PRs:
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