**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
return ui::cocoa::AtomBundleMover::Move(args);
}
bool App::IsInApplicationsFolder() {
  return ui::cocoa::AtomBundleMover::IsCurrentAppInApplicationsFolder();
}
#endif
mate::Handle<App> App::Create(v8::Isolate* isolate) {
  return mate::CreateHandle(isolate, new App(isolate));
}
void App::BuildPrototype(v8::Isolate* isolate,
                         v8::Local<v8::FunctionTemplate> prototype) {
  prototype->SetClassName(mate::StringToV8(isolate, "App"));
  auto browser = base::Unretained(Browser::Get());
  mate::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
      .SetMethod("quit", base::Bind(&Browser::Quit, browser))
      .SetMethod("exit", base::Bind(&Browser::Exit, browser))
      .SetMethod("focus", base::Bind(&Browser::Focus, browser))
      .SetMethod("getVersion", base::Bind(&Browser::GetVersion, browser))
      .SetMethod("setVersion", base::Bind(&Browser::SetVersion, browser))
      .SetMethod("getName", base::Bind(&Browser::GetName, browser))
      .SetMethod("setName", base::Bind(&Browser::SetName, browser))
      .SetMethod("isReady", base::Bind(&Browser::is_ready, browser))
      .SetMethod("whenReady", base::Bind(&Browser::WhenReady, browser))
      .SetMethod("addRecentDocument",
                 base::Bind(&Browser::AddRecentDocument, browser))
      .SetMethod("clearRecentDocuments",
                 base::Bind(&Browser::ClearRecentDocuments, browser))
      .SetMethod("setAppUserModelId",
                 base::Bind(&Browser::SetAppUserModelID, browser))
      .SetMethod("isDefaultProtocolClient",