This exposes the underlying IDBRequest of IDBCursor objects. It is a minor addition, exposing previously spec'd behavior.
Requests for cursors are different as they can succeed many times. When you call cursor.continue() the success of that operation is provided in the request returned by source.openCursor(). If I want to give an object store to another piece of code, I can just pass the object store. However, if I want to pass the cursor elsewhere, I also have to pass the related request. From this, it is reasonable to expose an IDBCursor's request object as an attribute.
Docs: No design docs were created for the implementation of this feature
Explainers: https://github.com/w3c/IndexedDB/issues/255#issue-416772452