Fix Deprecated SecKeyEncrypt Class (iOS)

[fujiokayu]

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This PR closes #1965

Additionally, I thought the first link for SecKey would be better in the Apple Developer documents, so I am modifying it together.

[cpholguera]

This help us a lot to keep the content up to date. Thank you very much for keeping an eye on this and sending us a fix @fujiokayu 🙏