fix(node:buffer): add missing atob and btoa exports

[IgorMinar]

https://nodejs.org/api/buffer.html#bufferatobdata
https://nodejs.org/api/buffer.html#bufferbtoadata

Fixes #2196

[jasnell]

Might be worth going ahead and including Blob here too

[IgorMinar]

@jasnell good catch. added.

[jasnell]

@IgorMinar ... can I ask you to rebase to deal with the merge conflict?

[IgorMinar]

@jasnell done. please note that I had to add eslint-disable-next-line bailouts into the code because our current typescript setup is not great, or at least I couldn't figure out how to make it all work with our custom d.ts files.

I suspect that we should really be using @types/node instead of our custom typings here but that was a much bigger change that I was willing to bite off in this PR.