The `security_level` stream option is only available as of OpenSSL
1.1.0, so we only set it for these versions. Older OpenSSL versions
do not have security levels at all.
This migrates all the tests using ext/openssl/tests/streams_crypto_method.pem
to the certificate generator, so we can easily adjust needed parameters.
In particular, this makes the cert security level 2 compatible.
However, we still need to downgrade security_level to 1 in a number
of tests, because they are testing TLS < 1.2 connections.
- All streams-related code now lives in xp_ssl.c. Previously
stream code was split across both openssl.c and xp_ssl.c
- Folded superfluous php_openssl_structs.h into xp_ssl.c
- Server-specific options now set on SSL_CTX instead of SSL
- Deprecate SNI_server_name ctx option
- Miscellaneous refactoring
