AnnotationType annTypeFromIdx(int idx) {
                var proxy = (AnnotationReferenceDataType) typesByIdx.get(idx);
                if (proxy == null) {
                    throw new IllegalArgumentException("Needed AnnotationType for idx "+idx+", found: "+typesByIdx.get(idx));
                }
                return proxy.getAnnotationType();
            }
One-shot configuration; should be called on a newly constructed manager
document/src/main/java/com/yahoo/document/DocumentTypeManagerConfigurer.java