**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
const JumpListItem& val) {
    mate::Dictionary dict = mate::Dictionary::CreateEmpty(isolate);
    dict.Set("type", val.type);
    switch (val.type) {
      case JumpListItem::Type::TASK:
        dict.Set("program", val.path);
        dict.Set("args", val.arguments);
        dict.Set("title", val.title);
        dict.Set("iconPath", val.icon_path);
        dict.Set("iconIndex", val.icon_index);
        dict.Set("description", val.description);
        break;
      case JumpListItem::Type::SEPARATOR:
        break;
      case JumpListItem::Type::FILE:
        dict.Set("path", val.path);
        break;
    }
    return dict.GetHandle();
  }
};
template <>
struct Converter<JumpListCategory::Type> {
  static bool FromV8(v8::Isolate* isolate,