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
I tried to stick as close to the existing code as possible.
Special:Notifications is slightly different from the overlay,
however. I made it add .mw-echo-unread class for consistency,
but that JS doesn't record seen time (it only loads older
entries), not does the CSS fadeout apply there (it marks
everything as read as soon as it's displayed, so different
behavior from overlay)
PS: I'm not sure about browser compat for the fadeout. But
even if some obscure browsers don't support this, meh. It's
not an "important" feature that can't be missed.
Bug: T94634
Change-Id: Ibb201823fb52ef8a3d5eaa39b0b724ede8d271d1
