**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/ui/atom_menu_model.cc
int command_id,
    ui::Accelerator* accelerator) const {
  return GetAcceleratorForCommandIdWithParams(command_id, false, accelerator);
}
AtomMenuModel::AtomMenuModel(Delegate* delegate)
    : ui::SimpleMenuModel(delegate), delegate_(delegate) {}
AtomMenuModel::~AtomMenuModel() {}
void AtomMenuModel::SetRole(int index, const base::string16& role) {
  int command_id = GetCommandIdAt(index);
  roles_[command_id] = role;
}
base::string16 AtomMenuModel::GetRoleAt(int index) {
  int command_id = GetCommandIdAt(index);
  if (base::Contains(roles_, command_id))
    return roles_[command_id];
  else
    return base::string16();
}
bool AtomMenuModel::GetAcceleratorAtWithParams(
    int index,
    bool use_default_accelerator,
    ui::Accelerator* accelerator) const {
  if (delegate_) {
    return delegate_->GetAcceleratorForCommandIdWithParams(
        GetCommandIdAt(index), use_default_accelerator, accelerator);
  }
  return false;
}
bool AtomMenuModel::ShouldRegisterAcceleratorAt(int index) const {