Scroll anchoring is hard to predict when resizing

When resizing a room's message view (such as by revealing/hiding the sidebar, or by resizing the app's window), the scroll anchor of the room jumps around.

I think an ideal behaviour here would be to make the scroll stick to the bottom of the view (not the top).

(I realize this might get complicated, but just from a user perspective, this is how I'd expect a well-behaving app to handle this.)