MDEV-7597 Expiration of user passwords

post-merge changes:
* handle password expiration on old tables like everything else -
  make changes in memory, even if they cannot be done on disk
* merge "debug" tests with non-debug tests, they don't use dbug anyway
* only run rpl password expiration in MIXED mode, it doesn't replicate
  anything, so no need to repeat it thrice
* restore update_user_table_password() prototype, it should not change
  ACL_USER, this is done in acl_user_update()
* don't parse json twice in get_password_lifetime and get_password_expired
* remove LEX_USER::is_changing_password, see if there was any auth instead
* avoid overflow in expiration calculations
* don't initialize Account_options in the constructor, it's bzero-ed later
* don't create ulong sysvars - they're not portable, prefer uint or ulonglong
* misc simplifications

mysql-test/suite/plugins/t/multiauth.test

@@ -130,7 +130,7 @@ drop user mysqltest1;
 #
 create user mysqltest1 identified via ed25519 as password("good") OR unix_socket OR mysql_native_password as password("works");
 show grants for mysqltest1;
---replace_regex /password_last_changed": [0-9]*/password_last_changed": 0/
+--replace_regex /password_last_changed": [0-9]*/password_last_changed": #/
 select json_detailed(priv) from mysql.global_priv where user='mysqltest1';
 select password,plugin,authentication_string from mysql.user where user='mysqltest1';
 flush privileges;