Allow partially releasing a record for TLS

Allow partially releasing a record for TLS

This enables the cleansing of plaintext to occur in the record layer and
avoids the need to cast away const above the record layer.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20404)