**Is your feature request related to a problem? Please describe.**

Currently, the only way to show the About panel on macOS is by creating a `{role: 'about'}` menu item and click it. I need to be able to show it manually.

**Describe the solution you'd like**

Electron already has the method, so it's just about exposing this to JS and documenting it:

https://github.com/electron/electron/blob/8ba271efba691357ab1970c1a553b4e019125574/atom/browser/browser_mac.mm#L376

Would also be useful to be able to pass in the panel options directly to the method to override the defaults.

I would call the method: `app.showAboutPanel(options)`

**Describe alternatives you've considered**

None.
atom/browser/api/atom_api_app.cc
bool override_argv = false;
  base::FilePath exec_path;
  relauncher::StringVector args;
  mate::Dictionary options;
  if (js_args->GetNext(&options)) {
    if (options.Get("execPath", &exec_path) | options.Get("args", &args))
      override_argv = true;
  }
  if (!override_argv) {
    const relauncher::StringVector& argv = atom::AtomCommandLine::argv();
    return relauncher::RelaunchApp(argv);
  }
  relauncher::StringVector argv;
  argv.reserve(1 + args.size());
  if (exec_path.empty()) {
    base::FilePath current_exe_path;
    base::PathService::Get(base::FILE_EXE, &current_exe_path);
    argv.push_back(current_exe_path.value());
  } else {
    argv.push_back(exec_path.value());
  }
  argv.insert(argv.end(), args.begin(), args.end());
  return relauncher::RelaunchApp(argv);
}
void App::DisableHardwareAcceleration(mate::Arguments* args) {