Allow (de-)serializing value classes if their backing property is serializable

[Martmists-GH]

What is your use-case and why do you need this feature?

For example, in Compose code, one might want to save the user's custom theme by serializing Colors. These are defined as value class Color(value: ULong) which should be trivial to (de-)serialize, as value classes guarantee a single-argument constructor and a single field to handle.

Describe the solution you'd like

Value classes are serialized as if serialize(myXTypeValue.value) was called, and deserialized like XType(deserialize(encValue))

[sandwwraith]

Even if the property is serializable, we still need the value class Color to be marked as @Serializable too. This comes from the fact that in constructions like List<Color> actual boxing happens (i.e. instantiation of a new Color instance, not just ULong). And to properly serialize/deserialize the class instance, a corresponding serializer have to be generated, since we can't write one serializer to deserialize all possible value classes — that's not how the compiler plugin works