Improve dynamic scaling of external Program icons

[akoch-yatta]

Program::getImageData is still relying on DPIUtil::getDeviceZoom to calculate the image scaling

[HeikoKlare]

@ShahzaibIbrahim since you are assigned, is this ticket in work?

[ShahzaibIbrahim]

Yes, just started working on it.

[fedejeanne]

I assume this one is targeted for 4.34 M3, right?

[HeikoKlare]

I see more urgent topics for M3, so I would not consider this mandatory. Still, this would be nice-to-have for M3, so adding the according tag would be fine for me.