As far as I know it has not been implemented. I thought it was a big deal at first but actually once you figure out other ways of doing it there’s absolutely no need for this.
When you’re filling in a sign up form or login form and you’re asked for a password, there is a prompt to open Bitwarden. Just open Bitwarden, add new credentials directly to Bitwarden (instead of typing them on the website) and save. Once saved, just click on the item in Bitwarden and it will automatically populate the sign up or login form.