Provide an ArrayCopy that can do shallow if possible

Oftentimes you need an array of a specific type. The easiest way to get that if you do not know the type (i.e. through templating) is to use ArrayCopy to copy to a known array type. However, it is wasteful to do this copy if the array is already of the correct type.

ArrayCopy.h should provide an alternate function (maybe called ArrayCopyShallowIfPossible) that will do a shallow copy if the array types match and a deep copy otherwise.