BindingOnDeleteOptions

What the binding's own delete callbacks are told.

Deliberately just the binding: onBeforeDelete fires because the *binding* record is going away, which happens for reasons that have nothing to do with either shape — an explicit deleteBinding, a store reset, a peer's edit arriving. When a *shape* is what is being deleted, the callback is onBeforeDeleteFromShape / onBeforeDeleteToShape, and it is told which.