This is a counterpart to bug 1091329, letting reads from reference members (object, string, any) of typed objects be optimized by Ion. For now this is pretty basic, assuming e.g. that 'any' members can have any value and that 'object' members can have any object or null. Pretty soon we'll need to expand TI so that it captures possible types of reference fields and elements, which should allow many barriers when reading these fields to be eliminated.