Allow scrolling throughout a window at ≥100% width

[postsolar]

Currently, if I use set-window-width to make a window >100%, it will always be clipped to the left, and I can't fix the view on an arbitrary section of the window.

TUI text editors could benefit from this being allowed (e.g. open many splits within a single window instead of opening new windows)

[YaLTeR]

I don't really know how this should work UX wise.

As a workaround, you can kinda "scroll" a wider than screen floating window by moving it around.