Add `ECDSAKey` support to `JWKS`

This patch was authored and released by @JaapWijnen.

• Allows to create JWK's using ECDSAKeys
• Allows use of ECDSAKeys with JWTSigner.
• Prevents a crash when using the .es384 curve for ECDSAKeys

let key = ECDSAKey.generate(curve: .p384)
let jwks = JWKS(keys: [
   JWK.ecdsa(.es384, identifier: JWKIdentifier(string: "token-kid"), x: key.parameters!.x, y: key.parameters!.y, curve: .p384)
])

let key = ECDSAKey.generate(curve: .p384)
let signer = JWTSigner.es384(key: key)