[UX] Allow cloning any user role (along with its permissions)

I was tasked to clone a user role for a site the other day. Here are the options one has:

• Execute a db query -> not user-friendly
• Create a new role, then manually set the same permissions as another role -> endless scrolling and clicking on checkboxes ; becomes worse the more contrib with additional permissions a site has (or many content types, since they also add multiple permissions); becomes even worse if the role you want to clone has many permissions assigned to it (might also become a victim of https://www.drupal.org/project/drupal/issues/1203766 if the site has many roles)
• https://www.drupal.org/project/duplicate_role (have not actually tested it) -> not ported to Backdrop

We should have a "Clone role" action.