PR #5251 adds support for CMS (RFC5662)

Hi everyone, I am new to the PHP development process, so please forgive me if I have this wrong. In PR #5251[1] I’ve created OpenSSL CMS functions that are nearly direct analogues to the openssl PKCS#7 functions.  Cryptographic Message Syntax is defined in RFC 5652[2], and is a follow-on to PKCS#7.  These functions are useful to developers who are creating or verifying PKI-based signatures (this is the case for me or anyone else who is implementing or deploying RFC 8520[3]), and there are other IoT services that are using CMS as well (not to mention certain modern mailing systems). There are one or two changes- one can specify the encoding format as an argument, for instance, and error out out the use of DETACHED with S/MIME encoding, as nobody seems to know what that would mean. I’ve been working with Jakub and others who have been very generous with their time on code reviews.  I would be grateful for any additional feedback you would have, with an eye toward merging this PR.  The PR is already marked as RFC I have not yet formalized that.(*) Best regards, Eliot (*) I tried adding an RFC page on the wiki, but sensibly, as I just created the account, the system did not permit me to do so. [1] https://github.com/php/php-src/pull/5251 [2] https://www.rfc-editor.org/rfc/rfc5652.html [3] https://www.rfc-editor.org/rfc/rfc8520.html

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