Support for selected item in canDragOver

[VeselyJan92]

Motivation:

I use LazyGrid for two types of items: categories and items. I am allow to reorder categories and items separetly but those two should never mixed up. My goal was is use canDragOver with return false if item A and B have different type (category, item). I hope it justifies the pull request.

Possible implementation:

  private fun Any?.type() = (this as String).split("_").first()

  val state = rememberReorderableLazyGridState(
      onDragEnd = { 
              from, to -> vm.onDragEnd()
      },
      canDragOver = { 
              draggedOver, dragging -> draggedOver.key.type() == dragging.key.type() 
      },
      onMove = { from, to ->
          val itemsBefore = data.activities.size + 1

          when {
              from.key.type() == "activity" && to.key.type() == "activity" -> vm.onMoveActivity(
                  from.index - 1,
                  to.index - 1
              )
              from.key.type() == "group" && to.key.type() == "group" -> vm.onMoveGroup(
                  from.index - itemsBefore,
                  to.index - itemsBefore
              )
              else -> throw IllegalArgumentException()
          }
      }
  )

Layout for reference:

[VeselyJan92]

@aclassen