Let caller of PageIsVerified() control ignore_checksum_failure

Let caller of PageIsVerified() control ignore_checksum_failure

For AIO the completion of a read into shared buffers (i.e. verifying the page
including the checksum, updating the BufferDesc to reflect the IO) can happen
in a different backend than the backend that started the IO. As
ignore_checksum_failure can differ between backends, we need to allow the
caller of PageIsVerified() control whether to ignore checksum failures.

The commit leaves a gap in the PIV_* values, as an upcoming commit, which
depends on this commit, will add PIV_LOG_LOG, which better fits just after
PIV_LOG_WARNING.

Reviewed-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20250329212929.a6.nmisch@google.com