Add account migration UI (#11846)

Fix #10736

- Change data export to be available for non-functional accounts
- Change non-functional accounts to include redirecting accounts

app/models/user.rb

@@ -168,7 +168,7 @@ class User < ApplicationRecord
   end
 
   def functional?
-    confirmed? && approved? && !disabled? && !account.suspended?
+    confirmed? && approved? && !disabled? && !account.suspended? && account.moved_to_account_id.nil?
   end
 
   def unconfirmed_or_pending?