Sets the check status of a menu item.
The check status of a menu item is cleared when the Editor restarts.
    using UnityEditor;
    using UnityEngine;
    public class CheckMenuTest: MonoBehaviour
    {
        // Add a menu item named "MenuTest" to MyMenu in the main menu.    
        [MenuItem("MyMenu/MenuTest")]
        static void DoSomething()
        {
            Debug.Log("A placeholder menu item.");         
        }
        
        // Add a menu item that you can click to add a check to the "MenuTest" menu item in MyMenu in the main menu. 
        [MenuItem("MyMenu/Check menu item")]
        static void CheckMenu()
        {
            Menu.SetChecked("MyMenu/MenuTest", true);
            Debug.Log("Checked 'MenuTest'");            
        }
        
        // Add a menu item that you can click to clear the check from the "MenuTest" menu item in MyMenu in the main menu. 
        [MenuItem("MyMenu/Clear check from menu")]
        static void ClearCheck()
        {
            Menu.SetChecked("MyMenu/MenuTest", false);
            Debug.Log("Cleared check from menu");
        }
    }