[struct_json, struct_xml, struct_yaml][feat]support alias

[qicosmos]

Why

support reflect with alias.

What is changing

Example

struct next_obj_t {
  int x;
  int y;
};

// struct alias name and fileds alias names.
REFLECTION_ALIAS(next_obj_t, "next", FLDALIAS(&next_obj_t::x, "w"),
                 FLDALIAS(&next_obj_t::y, "h"));

struct out_object {
  std::unique_ptr<int> id;
  std::string_view name;
  next_obj_t obj;
  REFLECTION_ALIAS(out_object, "qi", FLDALIAS(&out_object::id, "i"),
                   FLDALIAS(&out_object::name, "na"),
                   FLDALIAS(&out_object::obj, "obj"));
};

void test_alias() {
  out_object m{std::make_unique<int>(20), "tom", {21, 42}};
  std::string xml_str;
  iguana::to_xml(m, xml_str);

  std::cout << xml_str << "\n";

  out_object m1;
  iguana::from_xml(m1, xml_str);
  assert(m1.name == "tom");
  assert(m1.obj.x == 21);
  assert(m1.obj.y == 42);
}