[openssl/openssl] 6ebdbb: doc: improve documentation of EVP in-place encryption

[Matthias St. Pierre]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 6ebdbba76a45294e22006ede1442847cdee24f03
      https://github.com/openssl/openssl/commit/6ebdbba76a45294e22006ede1442847cdee24f03
  Author: Matthias St. Pierre <matthias.st.pierre at ncp-e.com>
  Date:   2023-12-12 (Tue, 12 Dec 2023)

  Changed paths:
    M doc/man3/EVP_EncryptInit.pod
    M doc/man7/provider-cipher.pod

  Log Message:
  -----------
  doc: improve documentation of EVP in-place encryption

The EVP interface explicitly allows in-place encryption/decryption,
but this fact is just 'partially' documented in `EVP_EncryptUpdate(3)`
(pun intended): the manual page mentions only operation failure in
case of 'partial' overlaps. This is not even correct, because
the check for partially overlapping buffers is only implemented
in legacy code paths.

Currently, in-place encryption/decryption is only documented for
RSA (`RSA_public_encrypt(3)`) and DES (`DES_ecb_encrypt(3)`), as
well as in the provider interface (`provider-cipher(7)`).

This commit amends `EVP_EncryptUpdate(3)` and `provider-cipher(7)`
to make the front-end and back-end documentation consistent.

Reviewed-by: Tomas Mraz <tomas at openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove at arm.com>
(Merged from https://github.com/openssl/openssl/pull/22875)