Background
For T325238, we want to allow privileged users to reveal the IP address used by a temporary account, ideally wherever a temporary account name is shown in the UI.
Temporary accounts may use multiple IP addresses over time, and in some places we only want to show the most relevant IP address (e.g. in a recent changes line, the IP that was used when that change was made).
Most instances of usernames being displayed on special pages etc are created by Linker::userLink.
What needs to be done
Linker::userLink should add a class for temporary user names, e.g. mw-tempuserlink, so that occurrences can be found easliy.
Linker::userLink should allow setting the HTML data attributes so that some context can be stored, which can be used to look up the most relevant IP address for a temporary account user (e.g. revision ID for history pages - T326392: IP Address Reveal on History page).
