MDEV-32500 Information schema leaks table names and structure to unauthorized users

standard table KEY_COLUMN_USAGE should only show keys where
a user has some privileges on every column of the key

standard table TABLE_CONSTRAINTS should show tables where
a user has any non-SELECT privilege on the table or on any column
of the table

standard table REFERENTIAL_CONSTRAINTS is defined in terms of
TABLE_CONSTRAINTS, so the same rule applies. If the user
has no rights to see the REFERENCED_TABLE_NAME value, it should be NULL

SHOW INDEX (and STATISTICS table) is non-standard, but it seems
reasonable to use the same logic as for KEY_COLUMN_USAGE.

sql/sql_parse.cc

@@ -7011,6 +7011,7 @@ static bool check_show_access(THD *thd, TABLE_LIST *table)
                      FALSE, FALSE))
           return TRUE; /* Access denied */
 
+    thd->col_access= dst_table->grant.privilege; // for sql_show.cc
     /*
       Check_grant will grant access if there is any column privileges on
       all of the tables thanks to the fourth parameter (bool show_table).