GRANT on a routine stores the user name in mysql.procs_priv re-encoded from latin1

Description

replace_routine_table() in sql/sql_acl.cc stores Host, Db, User, Routine_name and Grantor into mysql.procs_priv with &my_charset_latin1, while replace_table_table(), replace_column_table() and replace_db_table() use system_charset_info. For an account whose name has bytes outside ASCII the row holds the UTF-8 bytes converted a second time (D1 82 for "т" becomes C3 91 E2 80 9A). SHOW GRANTS shows the grant until the next FLUSH PRIVILEGES or restart; after the reload the row belongs to a user that does not exist and the account has lost EXECUTE on every routine. DROP FUNCTION / DROP PROCEDURE go through the same function, find only the re-encoded row, and a row corrected by hand stays behind; REVOKE ALL then fails with ER_NONEXISTING_GRANT. Unchanged since MySQL 5.5, present in 10.6 .. main.

Fix: store the five strings with system_charset_info, as the other grant tables do.

Release Notes

GRANT ... ON FUNCTION/PROCEDURE to an account with a non-ASCII user name no longer writes a double-encoded name into mysql.procs_priv; such grants now survive FLUSH PRIVILEGES and are removed by DROP of the routine.

How can this PR be tested?

set names utf8mb3;

create user 'юзер'@'localhost';

create function f() returns int deterministic return 1;

create procedure p() select 1;

grant execute on function test.f to 'юзер'@'localhost';

grant execute on procedure test.p to 'юзер'@'localhost';

grant select on test.* to 'юзер'@'localhost';

# The stored bytes must equal the bytes of the name, as in mysql.db

select hex(User) = hex('юзер') as ok, Routine_name from mysql.procs_priv where User like 'юзер' order by Routine_name;