Fix to module split-style to include packages for smallmodulesfor

[KristianAN]

SmallModulesFor as it was implemented did not include the required list of packages needed for the linker configuration

I was trying to update the js-bridge in bloop-core and I noticed I had messed this up in the last PR... The smallest modules for option requires a list of packages, see: https://github.com/scala-js/scala-js/blob/61e8525eebef3b17290c900c84fea9ba91dc540e/linker-interface/shared/src/main/scala/org/scalajs/linker/interface/ModuleSplitStyle.scala#L43.

So, I'm not sure how you'd structure this ADT in Scala 2, but I think this is an ok solution.

something like this

  val configOne: Config.ModuleSplitStyleJS =
    Config.ModuleSplitStyleJS.SmallModulesFor(List("one", "two"))

  val configTwo: Config.ModuleSplitStyleJS =
    Config.ModuleSplitStyleJS.SmallestModules

  val readConfigOne = jsoniter.readFromString[Config.ModuleSplitStyleJS](
    """{"splitStyle":"SmallModulesFor","packages":["one","two"]}"""
  )

  val readConfigTwo = jsoniter.readFromString[Config.ModuleSplitStyleJS](
    """{"splitStyle":"SmallestModules"}"""
  )
  println(readConfigOne)
  println(readConfigTwo)
  println(jsoniter.writeToString(configOne))
  println(jsoniter.writeToString(configTwo))

prints

SmallModulesFor(List(one, two))
SmallestModules
{"splitStyle":"SmallModulesFor","packages":["one","two"]}
{"splitStyle":"SmallestModules"}

this seems like an reasonable encoding to me.

[tgodzik]

Could you add some tests to make sure serializing/deserializing works?

[KristianAN]

Could you add some tests to make sure serializing/deserializing works?

Will do as soon as I have time!

[tgodzik]

Thanks!