MDEV-36870 Spurious unrelated permission error when selecting from table with default that uses nextval(sequence)

Lots of different cases, SELECT, SELECT DEFAULT(),
UPDATE t SET x=DEFAULT, prepares statements,
opening of a table for the I_S, prelocking (so TL_WRITE),
insert with subquery (so SQLCOM_SELECT), etc.

Don't check NEXTVAL privileges in fix_fields() anymore, it cannot
possibly handle all the cases correctly. Make a special method
Item_func_nextval::check_access() for that and invoke it from

* fix_fields on explicit SELECT NEXTVAL()
  (but not if NEXTVAL() is used in a DEFAULT clause)
* when DEFAULT bareword in used in, say, UPDATE t SET x=DEFAULT
  (but not if DEFAULT() itself is used in a DEFAULT clause)
* in CREATE TABLE
* in ALTER TABLE ALGORITHM=INPLACE (that doesn't go CREATE TABLE path)
* on INSERT

helpers
* Virtual_column_info::check_access() to walk the item tree and invoke
  Item::check_access()
* TABLE::check_sequence_privileges() to iterate default expressions
  and invoke Virtual_column_info::check_access()

also, single-table UPDATE in prepared statements now associates
value items with fields just as multi-update already did, fixes the
case of PREPARE s "UPDATE t SET x=?"; EXECUTE s USING DEFAULT.

sql/sql_insert.cc

@@ -1622,6 +1622,9 @@ static bool mysql_prepare_insert_check_table(THD *thd, TABLE_LIST *table_list,
     DBUG_RETURN(insert_view_fields(thd, &fields, table_list));
   }
 
+  if (table_list->table->check_sequence_privileges(thd))
+    DBUG_RETURN(TRUE);
+
   DBUG_RETURN(FALSE);
 }