gh-141801: Use accessors for ASN1_STRING fields in libssl (GH-141802)

* gh-141801: Use accessors for ASN1_STRING fields

While ASN1_STRING is currently exposed, it is better to use the
accessors. See https://github.com/openssl/openssl/issues/29117 where, if
the type were opaque, OpenSSL's X509 objects could be much more
memory-efficient.

* Update Modules/_ssl.c

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

* Update Modules/_ssl.c

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

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Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>