WebCrypto: fix algorithm availability in nginx modules

WebCrypto: fix algorithm availability in nginx modules

Previously, configure probes disabled Ed25519, X25519, and AES-KW in
nginx modules because the engine is configured with --no-openssl,
although WebCrypto uses nginx's OpenSSL and these algorithms were
available.

The fix is to detect 25519 APIs from OpenSSL headers and look up AES-KW
ciphers at runtime, removing the dependency on engine configuration
and direct references to wrap functions absent in some OpenSSL flavors.

This fixes #1139.