Documentation for Pkcs12::builder is incorrect for OpenSSL 3

[kazk]

PKCS#12 API updates

The default algorithms for pkcs12 creation with the PKCS12_create() function were changed to more modern PBKDF2 and AES based algorithms. The default MAC iteration count was changed to PKCS12_DEFAULT_ITER to make it equal with the password-based encryption iteration count. The default digest algorithm for the MAC computation was changed to SHA-256. The pkcs12 application now supports -legacy option that restores the previous default algorithms to support interoperability with legacy systems.
https://www.openssl.org/docs/man3.0/man7/migration_guide.html#PKCS-12-API-updates

OpenSSL 3 changed the default encryption algorithms to Nid::AES_256_CBC. openssl/openssl@762970b

rust-openssl/openssl/src/pkcs12.rs

Lines 74 to 79 in 15f263e

	/// Creates a new builder for a protected pkcs12 certificate.
	///
	/// This uses the defaults from the OpenSSL library:
	///
	/// * `nid_key` - `nid::PBE_WITHSHA1AND3_KEY_TRIPLEDES_CBC`
	/// * `nid_cert` - `nid::PBE_WITHSHA1AND40BITRC2_CBC`

A user reported a problem on macOS after a recent patch bump, and apparently the Security Framework fails to import modern PKCS#12. https://openradar.appspot.com/FB8988319

[sfackler]

Fixed in db2b0d7. I'm also adding support to load providers (like the legacy provider that would support the old algorithms), but need to figure out what to do about openssl/openssl#16970 first.