BACKUP SERVER of ENGINE=Aria

Implement ENGINE=Aria interface to the MDEV-14992 BACKUP SERVER statement.

This must involve acquiring some locks similar to how mariadb-backup does it.
The create table code in Aria was written before atomic ddl was implemented for create table. Aria first logs the create table information and then creates the tables files. If the log is readable, Aria can recreate the tables on recovery. There are improvements that could be made, documented in ma_create.cc, but there is no hurry in doing this as the servers ddl log functionality helps Aria to create tables crash safe.

The log can replay CREATE TABLE for an aria table, but it cannot recreate the .frm file
Note also rows for CREATE TABLE ... SELECT are not written to the transactional log. If the CREATE fails, the upper level is guaranteed to delete
the table, so there is no reason to log rows.