Win32: Add a font scaling option for NewUI.

It's a bit primitive, but it works. If the user selects a gigantic size, it can cause the text to go offscreen, but my graphics coding skills aren't really that great, so I wouldn't know where to look to prevent that. Defaults to 100% (no chance), and goes from 25% to 200% size.

Anyway, it's useful for if the user prefers a different font size (due to vision issues or preference), or if the user cranked up the DPI and suddenly finds themselves staring at really huge text and wants to bring it back down.