MDEV-21902 Nested JSON_ARRAYAGG in JSON_OBJECT should not get escaped.

Author: Alexey Botchkov

mysql-test/main/func_json.result

@@ -1243,6 +1243,9 @@ drop view v;
 select json_arrayagg(a order by a asc) from (select 1 a union select 2 a) t;
 json_arrayagg(a order by a asc)
 [1,2]
+select json_object('x', json_arrayagg(json_object('a', 1)));
+json_object('x', json_arrayagg(json_object('a', 1)))
+{"x": [{"a": 1}]}
 #
 # End of 10.5 tests
 #

mysql-test/main/func_json.test

@@ -761,6 +761,8 @@ drop view v;
 
 select json_arrayagg(a order by a asc) from (select 1 a union select 2 a) t;
 
+select json_object('x', json_arrayagg(json_object('a', 1)));
+
 --echo #
 --echo # End of 10.5 tests
 --echo #

sql/item.h

@@ -5325,6 +5325,7 @@ class Item_ref :public Item_ident,
   {
     return ref ? (*ref)->get_typelib() : NULL;
   }
+  bool is_json_type() { return (*ref)->is_json_type(); }
 
   bool walk(Item_processor processor, bool walk_subquery, void *arg)
   {