add an 'equals' method to ItemStack and compatibility w/ lua '==' (#12771)

Co-authored-by: rubenwardy <rw@rubenwardy.com>
Co-authored-by: sfan5 <sfan5@live.de>

src/script/lua_api/l_item.h

@@ -140,6 +140,9 @@ private:
 	// peek_item(self, peekcount=1) -> itemstack
 	static int l_peek_item(lua_State *L);
 
+	// equals(self, other) -> bool
+	static int l_equals(lua_State *L);
+
 public:
 	DISABLE_CLASS_COPY(LuaItemStack)