Implement inheritDiscriminator annotation

[pablf]

This is a different approach than #1112. The PR implements a inheritDiscriminator annotation to be used on case classes. If the parent class doesn't have a jsonDiscriminator annotation it will throw a compilation error when deriving a codec. When there is a jsonDiscriminator it will include this in the encoding with the name of the case class or the jsonHint.

I don't know if this is the exact use case of @alphaho, but I guess it might be encoding and decoding with different encoders for convenience when interacting between different parts of the code base. In these cases it might be easier to use something like this annotation. And this isn't a breaking change. What do you think @987Nabil?
fixes #1056
/claim #1056

The final code for the example of @alphaho would be

import zio.json._

@jsonDiscriminator("type")
sealed trait Animal
object Animal {
  @inheritDiscriminator @jsonHint("dog")
  case class Dog(name: String) extends Animal
  object Dog {
    implicit val dogCodec: JsonCodec[Dog] = DeriveJsonCodec.gen
  }
  
  @inheritDiscriminator @jsonHint("cat")
  case class Cat(name: String, weight: Double) extends Animal

  implicit val animalCodec: JsonCodec[Animal] = DeriveJsonCodec.gen
}

[987Nabil]

My personal opinion is, that this is a very special solution for a probably fringe use case that is also possible to have with more generic solution that already exists.
I would not merge this.
Maybe @fsvehla or @jdegoes can give their opinion too.

[jdegoes]

@pablf In your example, do you really need:

    implicit val dogCodec: JsonCodec[Dog] = DeriveJsonCodec.gen

or is this a copy/paste error?

[987Nabil]

@jdegoes the purpose was to have a Dog decoder that fails without the discriminator. How would this work, if you don't create one explicitly?

[pablf]

@jdegoes I think so. I don't understand completely the exact needs behind the feature request. Possibly the approach with map or transform should be enough for the use case of @alphaho.

[alphaho]

Very sorry for the late reply. While the inheritDiscriminator feels handy to me, I totally agree that this may be a special solution for such a use case. The approach from #1112 may be good enough for this case. When I came across the problem, I was so into the mindset that I want to generate the JsonCodec instance and I forgot that I can actually get one by mapOrFail on the parent's.
Thank you for both of your efforts by working on this issue! ❤️❤️ @987Nabil, @pablf