This commit introduces the following changes:
- Converters/codecs are now used based on generic type info.
- On WebMvc and WebFlux, kotlinx.serialization is enabled along
to Jackson because it only serializes Kotlin @Serializable classes
which is not enough for error or actuator endpoints in Boot as
described on spring-projects/spring-boot#24238.
TODO: leverage Kotlin/kotlinx.serialization#1164 when fixed.
Closes gh-26147