A class that extends LogFormatter should be created so that log events in the cu_private_event table can be displayed in Special:CheckUser's 'Get edits' results, Special:Investigate's timeline mode and the CheckUser API's 'Get edits' mode.
TODO:
- Implement a LogFormatter like class to format the action text for cu_private_event rows
- Create new message keys where appropriate to fit the standard format for log events in en.json and qqq.json
- Register the "checkuser-private-event" log type to use the newly created LogFormatter
- Test the newly created LogFormatter