/**
 * Convenience method for generating setState<FancyObject.sub.component>() from setState<FancyObject> callbacks.
 * If used in react, recommended that this be memoized.
 * 
 * @generic T should be a data-only object - nested objects are allowed but arrays, sets not supported
 * @param dataObject ANY instance of T, used only for its keys. MUST have all keys present
 * @param dataUpdater an updater function, which can be called as: dataUpdater(newT) or
 *   dataUpdater((oldT) => { return newTFromOldT(oldT) }) ; e.g. react setState() function.
 * @return a deep object that has the same keys as T, except each key also has a getUpdater() function;
 *   the getUpdater() on a subobject of T acts similarly to the dataUpdater<T> but to the subobject rather than the whole object.
 */