Add support for moving data from one epoch to the next

Add support for moving data from one epoch to the next

Sometimes data read by a record layer in one epoch is actually intended for
the next epoch. For example in a TLS with read_ahead, the read_ahead data
could contain a KeyUpdate message followed by application data encrypted
with new keys. Therefore we implement a mechanism for passing this data
across the epochs.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18132)