crypto: fix non-multiple of 8 in SubtleCrypto.deriveBits

[panva]

A WPT update made me look into this.

From the Node.js docs:

The Node.js implementation requires that length, when a number, is a multiple
of 8.

This was never true, instead the implementation returned the closest full byte length.

At the moment the browser implementations do the following

• Chromium aligns with this PR (and the updated WPTs)
• Firefox throws DataError
• Safari aligns with Node.js prior to this PR

There's no interop on this in the first place and there's even a pending decision around disallowing truncation in ECDH/X25519/X448 altogether.

Given that this is in my opinion a semver-major PRs that contain breaking changes and should be released in the next major version. change I would rather we only have to do one, i.e. disallow truncation when the spec changes in a major, or fix the implementation with this PR in a major. We've got time to figure out what to do in time for v24.x but i'm opening this to ping @nodejs/crypto and @nodejs/web-standards

[nodejs-github-bot]

Review requested:

• @nodejs/crypto

[panva]

@jasnell do you remember what lead to the current implementation which follows neither the docs nor the spec?

[jasnell]

@panva ... sorry! I just spotted this one!

do you remember what lead to the current implementation which follows neither the docs nor the spec?

I think it's just a bug.