So we're not abusing user preferences for the last seen time.
EchoSeenTime is a small wrapper around ObjectCache that handles the
fallback to user preferences during the transition.
All JavaScript code now needs to use mw.config.get('wgEchoSeenTime').
Bug: T95839
Change-Id: Ia45ba5e30eb4564250539d04d5886d2598ebd49a
* These tend to log errors many times in a row for the same few
users in any given time period. There is probably some usage
pattern issue in JS on top of the abuse of preferences for
such tracking state. In any case, this should help.
Bug: T95839
Change-Id: I4d57b1db43a63300a412a5de220b66081da754f1
