WebCrypto: Implement EdDSA and XDH; internal algorithms; wire provider

[ariawisp]

What

• Add WebCrypto implementations for EdDSA (Ed25519/Ed448) and XDH (X25519/X448).
• Update internal algorithms mapping for JS/WASM targets.
• Wire new algorithms in WebCryptoCryptographyProvider.
• No CI/build/test changes in this PR.

Why

• Provide JS/Web target support for EdDSA/XDH behind the new core APIs.

Notes

• Depends on Core APIs (EdDSA/XDH) — blocked by PR Core: Add EdDSA and XDH algorithm interfaces #109.
• Uses ASN.1 OID constants — blocked by PR ASN.1: RFC 8410 OIDs, ABSENT params, Unknown key preservation, SEQUENCE OF support #108 for DER/PEM-related paths.
• Availability varies by engine/browser; operations may fail at runtime if unsupported.
• Optional DER/PEM support can follow once ASN.1 changes merge (PR ASN.1: RFC 8410 OIDs, ABSENT params, Unknown key preservation, SEQUENCE OF support #108), if we choose to expose DER/PEM on this provider.