Add a descriptor kind for JsonContentPolymorphicSerializer #2697
Description
What is your use-case and why do you need this feature?
When you use JsonContentPolymorphicSerializer, it's impossible to specify a list of shapes you expect, while it's still useful for schema exporing.
Describe the solution you'd like
Probably, it should be a new descriptorKind in PolymorficKind and some utility function like
buildContentBasedDescriptor(options: List<SerialDescriptor>
to build it.