code: private Map<ExecutableElement, VariableElement> createMemberFields(
        AnnotationTypeDeclaration node, List<AnnotationTypeMemberDeclaration> members) {
      TypeElement type = node.getTypeElement();
      Map<ExecutableElement, VariableElement> fieldElements = new HashMap<>();
      for (AnnotationTypeMemberDeclaration member : members) {
        ExecutableElement memberElement = member.getExecutableElement();
        String propName = NameTable.getAnnotationPropertyName(memberElement);
        VariableElement field = GeneratedVariableElement.newField(
            propName, memberElement.getReturnType(), type);
        node.addBodyDeclaration(new FieldDeclaration(field, null));
        fieldElements.put(memberElement, field);
      }
      return fieldElements;
    }
docs: Create an instance field for each member.