Please add a non-standard `crypto.KeyedDigestStream` (or future-standard `crypto.subtle.sign` iterator input) for computing streaming HMACs

Web crypto doesn't support streaming hashes, and the current non-standard `crypto.DigestStream` is hash only (no keys), so it is impossible to compute a streaming HMAC without pulling in a JS implementation (which is more costly and less efficient).

Would love to have a similar `crypto.KeyedDigestStream` or even `crypto.HmacStream` since this is a very common signature in practice.

Thanks!
\- John

Update: `crypto.subtle.sign('HMAC', cryptoKey, bytesIter)` would be even better (see below)