This leaves menu applets running but invisible, and that's a regression
we need to take care of obviously. But not today, because it's getting
too late.
This option was renamed from scaled to stretch in DisplaySettings in
699ba84, but since WindowServer receives a plain string and was not
updated, it wouldn't recognize the new renamed value as a valid option.
Turns out sending plain strings via IPC and only mapping them to enum
values on the receiving end is brittle, we should probably update
Desktop::set_wallpaper_mode() to use an enum as well at some point.
Fixes#5006.
Now, `chres 640 480 2` can set the UI to HighDPI 640x480 at runtime. A
real GUI for changing the display factor will come later.
(`chres 640 480 2` followed by `chres 1280 960` is very fast since
we don't have to re-allocate the framebuffer since both modes use
the exact same number of physical pixels.)
