Move EncryptionStream to SubtleCrypto?

[twiss]

Hey 👋 Thanks for working on this, and apologies for not looking at the spec earlier!

As a high-level comment, I would argue EncryptionStream should live in the same namespace as crypto.subtle.encrypt. After all, it's equally "subtle" as that function, and people should be careful not to use unauthenticated algorithms by themselves, for example. So I think having some indication of that in the name (e.g. crypto.subtle.EncryptionStream) would be good.

Also, without necessarily advocating for doing so, if we ever want to add DecryptionStream, that would be even more "subtle" (since you have to be careful not to accidentally use unauthenticated data), so that should definitely have to live under SubtleCrypto, IMO.