When dealing with variable-length arrays, it is often useful to derive a var handle from a layout, and have the var handle accept a long coordinate - the logical index of the element at which access should occur.

Such a method used to exist - namely ValueLayout::arrayElementVarHandle, but it was dropped because (a) it wasn't general enough and (b) the more general version could be obtained via the combinator methods in the `MethodHandles` class.

However, accessing variable-length array is a common enough operation that deserves some dedicated API sugar.