Draft: Allow cancelling of list item drag operations with <kbd>Esc</kbd>

Note: see the original upstream MR. In theory, all this needs is test coverage.

What does this MR do and why?

Clean up sortable instances

Before, Sortable.js instances weren't cleaned up, which was a memory leak. It doesn't appear to have had any other consequences, but the next commit will rely on this cleanup behaviour being present.

Allow cancelling of list drag operations with Esc

This adds a Sortable.js plugin called RevertOnEscape which implements the ability cancel a drag operation by pressing the Escape key.

Part of #362955.

References

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• #362955

MR acceptance checklist

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Screenshots or screen recordings

simplescreenrecorder-2025-01-16_13.05.59

How to set up and validate locally

1. Open an issue
2. Add an un/ordered list to the description
3. Drag a list item
4. Press Esc
5. Observe drag is cancelled correctly
6. Do the same with an epic

Related to #362955