Replace "High-Res Display Scaling" with adjustable "Zoom" option

[mdusher]

Replaces the "High-Res Display Scaling" checkbox with a "Zoom" combo box so that the scaling is adjustable.

My purpose behind doing this is that I have a small 1440p display and the font is unreadable without squinting, but the current high-res display scaling option makes the window too large to fit on the display.