Polymorphism improvements

Polymorphic serialization received a couple of improvements in this release:

New subclassesOfSealed utility to automatically register sealed subclasses serializers in polymorphic modules (#2201). Use it in your SerializersModule when configuring a polymorphic hierarchy which contains both abstract and sealed classes. For example, when root of your hierarchy is an inteface, but most of your inheritors are sealed classes. The new function will register all known sealed subclasses for you, so you don’t need to list them one by one. This makes writing your SerializerModules much faster and simpler. Big thanks to Paul de Vrieze for contributing this feature.

Class discriminator conflict check rework (#3105). If a payload already contains a property with the same name as the configured discriminator (for example, type), it is called a class discriminator conflict. To produce a correct output and allow more inputs to be deserialized at the same time, the following changes were made:

• Conflicts introduced by JsonNamingStrategy transformations are now detected during serialization as well and will cause SerializationException. It also affects non-polymorphic classes.
• Conflicts from ClassDisciminatorMode.ALL_JSON_OBJECTS and SerializersModuleBuilder.polymorphicDefaultSerializer are also detected.
• It is allowed to deserialize such a conflicting key for both sealed and open polymorphic hierarchies. Previously, it was possible in the sealed hierarchies alone due to missing assertion. See #1664 for details.

General improvements

• Add .serialName to MissingFieldException for clearer diagnostics. (#3114)
• Generate unique Automatic-Module-Name entries for metadata JARs. (#3109)
• Revised ProGuard rules and added R8 tests. (#3041)
• CBOR: Improved error message when a byte string/array type mismatch is encountered. (#3052)

Bugfixes

• Fix the type in the BIGNUM_NEGATIVE tag name. (#3090)
• CBOR: Fix various bugs in the decoder implementation to be more strict and consistent with the specification.