It would be an advantage to have a realm_list_is_valid function exposed in the C-API, similarly to realm_object_is_valid.

A use case that justifies this addition is the handling of change listeners in the Kotlin SDK, e.g. when a list has been invalidated due to the owner object being deleted - right now we detect "access to invalidated list object" exceptions being thrown from Core when calling any of the list API methods to detect whether the list is valid.