Make layout more stable when changing screen dimensions

[Inwerpsel]

Currently, the position of the frame and full height frame changes quite a lot when you switch between screen sizes.

While this is inherently always going to happen to some extent, more could be done to make the transitions more gentle.

Challenges

• It's not feasible to make the page itself transition between the old and new dimensions, as the layout can completely change. Even if it's technically possible, it would be ridiculously expensive to render, especially if the full height frame is used. Also the transition would very often not have enough time to complete. So it's a given that this is an instant transition. And so most other transitions happening at the same time also need to be instant.
• When going through history, the screen dimensions can change very quickly multiple times. Since you can do this with the scroll wheel, or with a keyboard repeat that is arbitrarily fast, it can change at the monitor refresh rate. While regular input can also be done this fast (by pressing down key to go through the <select>), it's a lot less likely.