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/r/multiauth.result

@@ -123,8 +123,7 @@ json_detailed(priv)
         {
         }
     ],
-    "password_last_changed": 0,
-    "password_lifetime": -1
+    "password_last_changed": #
 }
 select password,plugin,authentication_string from mysql.user where user='mysqltest1';
 Password	plugin	authentication_string