**Is your feature request related to a problem? Please describe.**

MenuItem labels are meant to be short. There's currently no place to elaborate/clarify them.

**Describe the solution you'd like**

`NSMenuItem` supports a [`toolTip`](https://developer.apple.com/documentation/appkit/nsmenuitem/1514848-tooltip?language=objc) property. Would be nice if Electron could expose this.

From what I could find, [GTK (Linux) does not have any way to set tooltip on menu items](https://developer.gnome.org/gtk3/stable/GtkMenuItem.html).

No idea about Windows.

**Describe alternatives you've considered**

None.

**Additional context**

No.
shell/browser/api/atom_api_menu.h
v8::Local<v8::Value> val,
                     electron::AtomMenuModel** out) {
    
    if (val->IsNull()) {
      *out = nullptr;
      return true;
    }
    electron::api::Menu* menu;
    if (!Converter<electron::api::Menu*>::FromV8(isolate, val, &menu))
      return false;
    *out = menu->model();
    return true;
  }
};
}  
#endif