[REQ] [Kotlin] Use Kotlinx.serialization and Sealed Class for Polymorphism

[loicsiret]

It will be nice to use Kotlinx serialization and sealed class to deal with Polymorphism and custom discriminator.

Describe the solution you'd like

Instead of using interface as a Parent for polymorphism, we can take advantage of kotlin sealed class.
This will allow to use a JsonContentPolymorphicSerializer in the parent and create the Subtype mapping.

#14301