aead: API with separate buffers for input and output

[ia0]

Would it make sense to add the following methods to AeadInPlace (similarly for AeadMutInPlace) with default implementations based on the existing methods?

fn encrypt_mut(&self, nonce: &Nonce, aad: &[u8], plain: &[u8], cipher_tag: &mut [u8]) -> Result<()> { ... }
fn encrypt_mut_detached(&self, nonce: &Nonce, aad: &[u8], plain: &[u8], cipher: &mut [u8]) -> Result<Tag> { ... }

fn decrypt_mut(&self, nonce: &Nonce, aad: &[u8], cipher_tag: &[u8], plain: &mut [u8]) -> Result<()> { ... }
fn decrypt_mut_detached(&self, nonce: &Nonce, aad: &[u8], cipher: &[u8], tag: &Tag, plain: &mut [u8]) -> Result<()> { ... }

This would add support (without extra copies or allocation) for implementations that don't support aliasing input and output. They would implement the _mut version and use a copy to implement the _in_place version using the _mut version.