LedgerTransaction is not meant to be created directly from client code, but it being a data class means we will expose new copy methods as new properties are added. The existing copy methods that we've exposed since V3 are deprecated, and equals and hashCode have been updated to be based just on id.
The primary c'tor has been clearly marked as the class' wire format, and so the internal stuff has been moved out. The references property cannot be made nullable and so DeprecatedConstructorForDeserialization is used instead.
