**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
std::vector<JumpListCategory> categories;
  bool delete_jump_list = val->IsNull();
  if (!delete_jump_list &&
      !mate::ConvertFromV8(args->isolate(), val, &categories)) {
    args->ThrowError("Argument must be null or an array of categories");
    return JumpListResult::ARGUMENT_ERROR;
  }
  JumpList jump_list(Browser::Get()->GetAppUserModelID());
  if (delete_jump_list) {
    return jump_list.Delete() ? JumpListResult::SUCCESS
                              : JumpListResult::GENERIC_ERROR;
  }
  
  if (!jump_list.Begin())
    return JumpListResult::GENERIC_ERROR;
  JumpListResult result = jump_list.AppendCategories(categories);
  
  
  if (!jump_list.Commit()) {
    LOG(ERROR) << "Failed to commit changes to custom Jump List.";
    
    
    
    if (result == JumpListResult::SUCCESS)
      result = JumpListResult::GENERIC_ERROR;
  }
  return result;
}
#endif  
void App::GetFileIcon(const base::FilePath& path, mate::Arguments* args) {