GcmAuthenticatedCryptographicTransform
Applies a GCM encryption or decryption to the input, decided by TransformMode,
and writes the result to output.
An encrypted input or output contains the nonce, then ciphertext, then tag, while the unencrypted input or
output only contains plaintext. Plaintext and ciphertext have equal length when using GCM, though the input
and output will not, given one has the nonce and tag attached.