Generate function can now take values as parameters

[5cript]

generate on observed can now take a function that takes the observed values as arguments.

div {
  class_ = observe(val1, val2).generate([](std::string const& str1, std::string const& str2) {
    return fmt::format("{} {}", str1, str2);
  });
}

Other smaller fixes and changes:

• Added option to forward JSON_DIAGNOSTICS to nui targets for nlohmann_json. (NUI_JSON_DIAGNOSTICS)
• Improved performance for some attributes by using fmt to generate the string.
• Fixed ResizeObserver destructor by calling disconnect.
• Fixed DragEvent by removing hasOwnProperty check, because it never has the property as 'dataTransfer', its from a prototype.