PLEASE NOTE THAT THIS DIFF AND SUBSEQUENT DIFFS IN THIS STACK WILL NOT BE LANDED UNTIL MORE OF THE REDESIGN IS READY SINCE THIS WILL CAUSE REGRESSIONS IN PROD
Now that we have the previously selected users stored in the previouslySelectedUsers map, we should display them in the add users list.
Linear task: https://linear.app/comm/issue/ENG-5960/selected-users-section
Depends on D10820