Convert SSL_SESSION_ASN1 to use size specific integers

This increases portability of SSL_SESSION files between architectures
where the size of |long| may vary.  Before this, SSL_SESSION files
produced on a 64-bit long architecture may break on a 32-bit long
architecture.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3088)