Follow on work from SERVER-129519. We should look into making the sizeStats cursor less disruptive for the WiredTigerCursor class.

The change itself had some challenges with layering, with the recovery unit trying to perform two jobs, we moved that layering down but that had the side effect of adding more context to the WiredTigerCursor

This ticket is fairly low priority, the feature itself is experimental and may be removed at a later date.

 cc: gregory.wlodarek@mongodb.com