Use new `generatedKotlin` API in Kotlin 2.3

[yogurtearl]

Use the new generatedKotlin API in Kotlin 2.3
https://kotlinlang.org/docs/whatsnew-eap.html#new-api-for-registering-generated-sources-in-gradle-projects

It is experimental, so maybe have optional support for now?