**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
content::RenderFrameHost* opener,
    const GURL& opener_url,
    const GURL& opener_top_level_frame_url,
    const GURL& source_origin,
    content::mojom::WindowContainerType container_type,
    const GURL& target_url,
    const content::Referrer& referrer,
    const std::string& frame_name,
    WindowOpenDisposition disposition,
    const blink::mojom::WindowFeatures& features,
    const std::vector<std::string>& additional_features,
    const scoped_refptr<network::ResourceRequestBody>& body,
    bool user_gesture,
    bool opener_suppressed,
    bool* no_javascript_access) {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  content::WebContents* web_contents =
      content::WebContents::FromRenderFrameHost(opener);
  if (web_contents) {
    auto api_web_contents = WebContents::From(isolate(), web_contents);
    
    if (!api_web_contents.IsEmpty()) {
      api_web_contents->OnCreateWindow(target_url, referrer, frame_name,
                                       disposition, additional_features, body);
    }
  }
  return false;
}
void App::AllowCertificateError(