Investigate and fix JWK parsing for WebCryptoAPI

There are so many failing WPT tests relating to JWK parsing that it likely points to some issues with our implementation. We should look at our implementation and see if it needs fixing.

Examples:
- Invalid 'crv' field: importKey(jwk(private), {name: ECDSA, namedCurve: P-256}, true, [sign])
- Good parameters with JWK alg Ed25519: Ed25519 (jwk, object(kty, crv, x), {name: Ed25519}, true, [verify])
- Invalid key pair: importKey(jwk(private), {name: Ed25519}, true, [sign])