hwdb: map zoomin/out keys to up/down

hwdb: map zoomin/out keys to up/down

Some keyboards come with a zoom see-saw or rocker which until now got
mapped to the Linux "zoomin/out" keys in hwdb. However, these keycodes
are not recognized by any major desktop. They now produce Up/Down key
events so that they can be used for scrolling.

The internet is full of instructions how to "unbreak" these keys, e. g.

  https://askubuntu.com/questions/471802/make-the-zoom-slider-of-microsoft-natural-ergonomic-keyboard-4000-and-7000-scrol
  https://unix.stackexchange.com/questions/322075/how-to-get-ms-natural-ergonomic-4000-slider-work-on-linux-mint

So let's make it official. But keep their physical meaning in comments
in case desktops start to do something useful with them at some point.

Thanks to Finn Christiansen for the original patch!

Replaces #6953