Rule: Check `evt.defaultPrevented` before and call `evt.preventDefault()` after handling `editor-drop`/`editor-paste` events

[RyotaUshio]

From the developer documentation (editor-drop, editor-paste):

Check for evt.defaultPrevented before attempting to handle this event, and return if it has been already handled. Use evt.preventDefault() to indicate that you've handled the event.

This rule would enforce such handling.