Since AES-GCM-SIV is nonce-misuse resistant, this encryption mode
could also be used in situations where the nonce is user provided.
However, because of lack of concrete use cases this is currently not
implemented.

PiperOrigin-RevId: 222051134
GitOrigin-RevId: 353fc02f64accde521a98bb7d774b8e1b015d275