In `st`, we can do this by using `ST_PARAM_*`. In the other code files,
just use `G_PARAM_STATIC_STRINGS` directly.
This is just a minor convenience to prevent a few unnecessary string
copies.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/646
The same code for reading the current magnifier state is repeated in both
shell-recorder, shell-screenshot and magnifier itself.
So to move this inside a property of st-settings so that we can refer to it
all over the places removing duplications.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/473