Broken Lead Warner for 1.21.6

Simple 1.21.6 port - nothing has been added or changed.

Note: As of now, if you connect a lead to another entity (e.g. a Happy Ghast holding a boat) and it breaks, it does not alert you because it isn't considered yours anymore. I want to look into adding support for this in the future, however, there's no guarantees as it may not even be possible while remaining fully client-side.

Beyond that, enjoy!