MDEV-23656 view: removal of parentheses results in wrong result

Item_ref should have the precedence of the item it's referencing

mysql-test/r/precedence_bugs.result

+#
+# MDEV-23656 view: removal of parentheses results in wrong result
+#
+create table t1 (a int, b decimal(10,2));
+insert into t1 values (1, 10.2);
+create view v1 as select avg(b) / (2 + a) from t1;
+show create view v1;
+View	v1
+Create View	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS select avg(`t1`.`b`) / (2 + `t1`.`a`) AS `avg(b) / (2 + a)` from `t1`
+character_set_client	latin1
+collation_connection	latin1_swedish_ci
+drop view v1;
+drop table t1;

mysql-test/t/precedence_bugs.test

+
+--echo #
+--echo # MDEV-23656 view: removal of parentheses results in wrong result
+--echo #
+create table t1 (a int, b decimal(10,2));
+insert into t1 values (1, 10.2);
+create view v1 as select avg(b) / (2 + a) from t1;
+query_vertical show create view v1;
+drop view v1;
+drop table t1;

sql/item.h

@@ -4541,7 +4541,11 @@ class Item_ref :public Item_ident
   {
     (*ref)->restore_to_before_no_rows_in_result();
   }
-  virtual void print(String *str, enum_query_type query_type);
+  void print(String *str, enum_query_type query_type);
+  enum precedence precedence() const
+  {
+    return ref ? (*ref)->precedence() : DEFAULT_PRECEDENCE;
+  }
   void cleanup();
   Item_field *field_for_view_update()
     { return (*ref)->field_for_view_update(); }