Array::deep_clone is not appropriate

[hackwaly]

The Array::deep_clone currently implemented as https://github.com/moonbitlang/core/blob/b231cb9098d9f98b5dd6e3a195aadfd899edf2b5/builtin/array.mbt#L165-L171

In my opinion. Deep clone should looks like this:

fn deep_clone[T : Clonable](self : Array[T]) -> Array[T] {
  // ...
}

I suggest to change deep_clone to copy or shallow_copy or clone.