Use fmt for formatting validation errors

Code that converts var-args to fmt formatted string:

```
#include <fmt/format.h>

template<typename... Args>
const std::string make_string(const char* str, Args... args)
{
  return fmt::format(str, args...);
}
```

```xml
<depend>fmt</depend>
```

```cmake
find_package(fmt REQUIRED)
target_link_libraries(<library_name> fmt::fmt)
```