Currently, AutoScaleMethod "nearest" is used by default, leading to
jagged image scaling results. The method "smooth" is only used on GTK
with a fractional scaling value not being a multiple of 100.
The reason for not using "smooth" scaling on all platform was a bug
regarding icon transparency that has long been resolved.

With this change, AutoScaleMethod "smooth" is used by default in
fractional scaling scenarios (i.e., with deviceZoom not being an integer
multiple of 100) and when using monitor-specific scaling on Windows. To
still use "nearest" in these scenarios, it can be activated via system
property.