Don't check kind if needn't type discriminator for enum and primitive

[SettingDust]

What is your use-case and why do you need this feature?
Output the enum and primitive correctly.
If we add a PrimitiveKind descriptor to a subclass of polymorphic serializer. There is error #1486
If we add a wrapper for the primitive(#1252 (comment)). The result will be wrapped even if the classDiscriminatorMode = ClassDiscriminatorMode.NONE like below.

{
  "data": {
    "value": "FOO"
  }
}

Related: #1252 #1486

Describe the solution you'd like
https://github.com/Kotlin/kotlinx.serialization/blob/master/formats/json/commonMain/src/kotlinx/serialization/json/internal/Polymorphic.kt#L41
Avoid failing if needn't discriminator for checkKind. Add a condition in checkKind or encodePolymorphically

val kind = actual.descriptor.kind
if(needDiscriminator || (kind !is SerialKind.ENUM && kind !is PrimitiveKind)) checkKind(kind )

[sandwwraith]

Can you post an example code and incorrect output, please?

[SettingDust]

The same error with #1486.
This is a FR for allowing enum and primitive in polymorphic if needn't the type information.
I'll append the example to body

[sandwwraith]

if needn't the type information.

You always need type information when deserializing polymorphic type. Are you talking about serialization-only use case?

[SettingDust]

You always need type information when deserializing polymorphic type. Are you talking about serialization-only use case?

https://github.com/Kotlin/kotlinx.serialization/blob/master/formats/json/commonMain/src/kotlinx/serialization/json/JsonConfiguration.kt#L78-L84 said it's a use case.

[SettingDust]

https://github.com/Kotlin/kotlinx.serialization/blob/master/formats/json/commonMain/src/kotlinx/serialization/json/internal/PolymorphismValidator.kt#L45 Need modify as well