Avoid cloning plaintext on AES encrypt

[ernieturner]

In our AES encrypt method in crypto/aes.rs, we're cloning the provided plaintext vector so we can resize it to add 16 bytes to it to support adding on the GCM auth tag. As people could be encrypting large large documents with the SDK, doing a clone is bad. We need to figure out a way to avoid it.

It would also be nice to see if we can have the various AES methods take slices instead of vecs as some inputs to encrypt have to be copied to get them into vectors. See this code review comment

[ernieturner]

Look into changing interface to take ownership of a Vector, resize it, and then return it.