[Notifications] Always transfer state from notification to be replaced

Also keep created() with the original notification.

As per spec a notification must be replaced atomically with no visual cues. Transfer over properties that might cause this, such as unread showing the bell again.

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the server must atomically (ie with no flicker or other visual cues) replace the given notification with this one.

I would consider shifting about to be a visual cue. An application must issue a new notification for it to move to the top again.

• issued notification 1, issued notification 2, updated notification 1. notification 1 remained in the same position
• issued a notification, hovered the popup, opened history, clicked a button: no longer had the bell suddenly plop up while the history was open