Mark everything as read when user dismisses "go to first unread message" banner

Keeping up with a room is a bit of a hassle right now: when you click the "go to first unread banner" you move up, maybe to weeks-old messages, and then you have to keep scrolling down until you reach the last message if you want to have everything marked as read.

To avoid this, I would like it if dismissing the banner marked the whole room as read.