Add object form of Ed25519 overload for SubtleCrypto#generateKey

[steveluscher]

As a follow up for #1594, I'd like to add the object form of the Edwards curve identifier ({ name: "Ed25519" }) to complement the string form ("Ed25519").

This will prevent having to constantly refine the return type of generateKey when all this API ever returns is a CryptoKeyPair when used with this algorithm.

const key = await crypto.subtle.generateKey(
  { name: 'Ed25519' },
  false, /* extractable */
  ['sign', 'verify'],
) as CryptoKeyPair;

See #1594 for more.

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[saschanaz]

LGTM for now, but this still needs more general form.

[github-actions]

Merging because @saschanaz is a code-owner of all the changes - thanks!