More abilities, refactor stealing held items

PkmnLib.Dynamic/ScriptHandling/Script.cs

@@ -812,6 +812,13 @@ public abstract class Script : IDeepCloneable
     {
     }
 
+    /// <summary>
+    /// This function allows a script to prevent a held item from being stolen by an effect such as Thief or Covet.
+    /// </summary>
+    public virtual void PreventHeldItemSteal(IPokemon pokemon, IItem heldItem, ref bool prevent)
+    {
+    }
+
     /// <summary>
     /// This function allows a script to run after a held item has changed. 
     /// </summary>