When one use scaling set by gnome tools (gsettings or
gnome-tweak-tool), gsd-xsettings must be running to apply the change
also to other applications.
This include auto scaling on HiDPI screens.
This commit fixes non-uniform behaviour on different VM types.
QubesOS/qubes-issues#3108
Usage of _static_ files (dropins) to override some of autostart entries
(enable/disable them in appropriate VM types) is much simpler and less
error prone than automatic generators.
Handling code is implemented in qubes-session-autostart, which is called
from qubes-session.
qubesos/qubes-issues#1151
