message: Add to_printf_arg() for classes with to_string()
diff: namespace vcpkg::Strings::details
  {
  + template<class T>
  + auto to_printf_arg(const T& t) -> decltype(t.to_string())
  + {
  + return t.to_string();
  + }
  +
  inline const char* to_printf_arg(const std::string& s)
  {
  return s.c_str();
  