user name changes: fix permission inconsistencies.

* Let moderators see name changes for deleted users on the user name
  change requests index and show pages. Before they could see name changes
  for deleted users on user profiles, but not on the user name changes index.

* Let members see previous names on profile pages. Before they could see
  previous names on the user name changes index, but not on profile pages
  (ref: #4382).

app/models/user_name_change_request.rb

@@ -9,7 +9,7 @@ class UserNameChangeRequest < ApplicationRecord
   after_create :update_name!
 
   def self.visible(user)
-    if user.is_admin?
+    if user.is_moderator?
       all
     elsif user.is_member?
       where(user: User.undeleted)

app/policies/user_name_change_request_policy.rb

@@ -4,7 +4,7 @@ class UserNameChangeRequestPolicy < ApplicationPolicy
   end
 
   def show?
-    user.is_admin? || (user.is_member? && !record.user.is_deleted?) || (record.user == user)
+    user.is_moderator? || (user.is_member? && !record.user.is_deleted?) || (record.user == user)
   end
 
   def permitted_attributes

app/presenters/user_presenter.rb

@@ -146,10 +146,4 @@ class UserPresenter
       []
     end
   end
-
-  def previous_names(template)
-    user.user_name_change_requests.visible(CurrentUser.user).map do |req|
-      template.link_to req.original_name, req
-    end.join(", ").html_safe
-  end
 end

app/views/users/_statistics.html.erb

@@ -191,11 +191,19 @@
         <td><%= presenter.feedbacks(self) %></td>
       </tr>
       
-      <% if CurrentUser.is_moderator? && presenter.previous_names(self).present? %>
-        <tr>
-          <th>Previous Names</th>
-          <td><%= presenter.previous_names(self) %></td>
-        </tr>
+      <% if policy(UserNameChangeRequest.new(user: user)).show? %>
+        <% user.user_name_change_requests.visible(CurrentUser.user).tap do |changes| %>
+          <% if changes.present? %>
+            <tr>
+              <th>Previous Names</th>
+              <td>
+                <%= changes.map do |change| %>
+                  <% link_to change.original_name, change %>
+                <% end.join(", ").html_safe %>
+              </td>
+            </tr>
+          <% end %>
+        <% end %>
       <% end %>
 
       <% if CurrentUser.id == user.id %>