Function get_key_length 

pub(crate) fn get_key_length(
    normalized_derived_key_algorithm: &SubtleAesDerivedKeyParams,
) -> Result<Option<u32>, Error>

https://w3c.github.io/webcrypto/#aes-ctr-operations-get-key-length https://w3c.github.io/webcrypto/#aes-cbc-operations-get-key-length https://w3c.github.io/webcrypto/#aes-gcm-operations-get-key-length https://w3c.github.io/webcrypto/#aes-kw-operations-get-key-length https://wicg.github.io/webcrypto-modern-algos/#aes-ocb-operations-get-key-length