Add ChunkBuilder#isEmpty method

[kyri-petrou]

Being able to know whether the ChunkBuilder currently contains any elements can be quite useful in some cases, e.g.,

def collectFooAndBar(): ChunkBuilder[String] = {
  val builder1 = new ChunkBuilder.Obj[String]
  val builder2 = new ChunkBuilder.Obj[String]

  foo(builder1)
  bar(builder2)
  
  if (builder1.isEmpty) builder2
  else if (builder2.isEmpty) builder1
  else builder1 ++= builder2.result() 
}

Note that MiMa didn't like me adding an abstract method on ChunkBuilder (even though it's a sealed abstract class, and just to play it safe I added another final class extension to ChunkBuilder, and only the final classes have the isEmpty method. Let me know if you think it's okay to add the abstract method and I'll do that

[guizmaii]

Why did you choose Obj as the name for this class? Why not something like ChunkBuilderLive for example? 🤔

[kyri-petrou]

Mostly because it's meant for objects (i.e., non-primitives). But yeah Obj doesn't sound too great. We could go with a similar name as ArrayBuilder and use OfRef

[guizmaii]

Oh ok I understand now. Thanks! I let you choose what you prefer :)