Optimize multi-dimensional array creation

[retronym]

We could consider using:

  def ofDim[T](n1: Int, n2: Int)(implicit tag: ClassTag[T]): Array[Array[T]] = {
    java.lang.reflect.Array.newInstance(tag.runtimeClass, n1, n2).asInstanceOf[Array[Array[T]]]
  }

Or we could introduce an additional constructor to Array that allows multiple dimensions to be specified and then update the backend to emit multinewarray.

@DarkDimius implemented something along these lines in dotty:

scala/scala3@b2215ed
lampepfl/scala@4bf9759