**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
#if defined(OS_LINUX)
  std::unique_ptr<base::Environment> env(base::Environment::Create());
  env->SetVar("CHROME_DESKTOP", desktop_name);
#endif
}
std::string App::GetLocale() {
  return g_browser_process->GetApplicationLocale();
}
void App::OnSecondInstance(const base::CommandLine::StringVector& cmd,
                           const base::FilePath& cwd) {
  Emit("second-instance", cmd, cwd);
}
bool App::HasSingleInstanceLock() const {
  if (process_singleton_)
    return true;
  return false;
}
bool App::RequestSingleInstanceLock() {