Rework SLRU I/O errors handle - Mailing list pgsql-hackers

Hi!

Beginning of the discussion is here [0].

Historically, the SLRU module was designed to handle 32-bit
transactions. However, it is now utilised for handling a variety of
object types, like TransactionId, MultixactId, MultiXactOffset,
QueuePosition, and so on. But the IO error reporting system is still
designed to support 32-bit XIDs exclusively.

The proposed patchset allows us to define a "custom" callback to
improve error messages.

The first two commits add a callback and test case. The subsequent ones
improve I/O error messages. The last one adds the XID epoch to the error
message. It's purely optional, but I think it would be useful.

[0] https://www.postgresql.org/message-id/CACG%3Dezbwy1zargXDNPeYXxZwRW3jXu_aD%3DrcG-7dc4fw7Y9Ojw%40mail.gmail.com