Refs. #3522. The core problem is the same as for groups/features: we can't
allow empty trusts when they're unmarshalled from JSON. But unlike others we
can't easily differentiate missing any value with other cases because the
default value for WildPermissionDescs is a valid thing. Adding an additional
field makes it invalid and we can build around it. Other options are
implementing custom UnmarshalJSON for Manifest (too much for this) or making
Trusts a pointer (an option, but can fail in too many ways).
Signed-off-by: Roman Khimov <roman@nspcc.ru>
We have a lot of native contract types that are converted to stack items
before serialization, then deserialized as stack items and converted back to
regular structures. stackitem.Convertible allows to remove a lot of repetitive
io.Serializable code.
This also introduces to/from converter in testserdes which unfortunately
required to change util tests to avoid circular references.
Frequently one needs to check if struct serializes/deserializes
properly. This commit implements helpers for such cases including:
1. JSON
2. io.Serializable interface
