Force password entry UI

[kklas]

We want to add the ability to export private keys to our Snap (https://suisnap.com). While technically possible, normally you’d require the user to re-enter the password for such a request, which is not possible currently because there is no API method within the Snap to force the password entry UI. I propose that a “request password entry” API call is added so that passwords can be safely exported and showed to the user within the Snap UI.