**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
public:
  AppIdProcessIterator() : base::ProcessIterator(nullptr) {}
 protected:
  bool IncludeEntry() override {
    return (entry().parent_pid() == base::GetCurrentProcId() ||
            entry().pid() == base::GetCurrentProcId());
  }
};
IconLoader::IconSize GetIconSizeByString(const std::string& size) {
  if (size == "small") {
    return IconLoader::IconSize::SMALL;
  } else if (size == "large") {
    return IconLoader::IconSize::LARGE;
  }
  return IconLoader::IconSize::NORMAL;
}
int GetPathConstant(const std::string& name) {