Do not write garbage or disable page checksums for temporary tables

As noted in MDEV-14925, InnoDB disables page checksums for temporary tablespaces. If pages are corrupted in the file system, InnoDB would fail to notice it, and it could crash in some ‘random’ place much later.

Even worse, InnoDB is not clearing previous page contents when allocating a page for a temporary tablespace (table or undo log data). Because the temporary tablespace (ibtmp1) is currently not encrypted, this could leak unrelated information from encrypted tablespaces to the temporary tablespace file.

Fixing these issues might slightly reduce the performance of temporary tables in InnoDB. Performance-conscious users should probably CREATE TEMPORARY TABLE…ENGINE=Aria in the first place. But, the application logic should take into account that ROLLBACK is a no-op in ENGINE=Aria.