Module with serializers

[JakeWharton]

For use in kotlinx.serialization.

While this somewhat abandons the premise of being implementation-only, it's nice to send these types to the serialization layer without the need for an otherwise-pointless asList() and having them deserialized on the other size to something efficient.

[JakeWharton]

It is still conceivable that platform-specific serialization models could use these.

However, things like default values and the lack of serialization of defaults has surprising effects. For one, you always have to allocate to get an empty array to compare against. But beyond that, the serialization-generated equals is unlikely to work because that's a Kotlin concept.