Because when it's inherited, it's not the same symbol anymore.

In the IR, you are only ever allowed to call Scala methods on `ClassType`s. But arrays are `ArrayType` (and `Object` is `AnyType`). So you have to go through helpers (or primitives) to call methods of non-`ClassType` symbols.

I could have special-cased `clone__O` for `ArrayType`, but that would prevent to re-encode `ArrayType`s as JS Typed Arrays if we so wish in the future.