We're planning to implement a feature that allows adding required fields for existing users. This PR does some preparatory refactoring to make that possible. There should be no changes to existing behaviour. Just a small update to the admin UI.
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
