**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.cc
return model_->GetIndexOfCommandId(command_id);
}
int Menu::GetItemCount() const {
  return model_->GetItemCount();
}
int Menu::GetCommandIdAt(int index) const {
  return model_->GetCommandIdAt(index);
}
base::string16 Menu::GetLabelAt(int index) const {
  return model_->GetLabelAt(index);
}
base::string16 Menu::GetSublabelAt(int index) const {
  return model_->GetSublabelAt(index);
}
base::string16 Menu::GetAcceleratorTextAt(int index) const {
  ui::Accelerator accelerator;
  model_->GetAcceleratorAtWithParams(index, true, &accelerator);
  return accelerator.GetShortcutText();
}
bool Menu::IsItemCheckedAt(int index) const {
  return model_->IsItemCheckedAt(index);
}
bool Menu::IsEnabledAt(int index) const {
  return model_->IsEnabledAt(index);
}
bool Menu::IsVisibleAt(int index) const {
  return model_->IsVisibleAt(index);
}
bool Menu::WorksWhenHiddenAt(int index) const {