Per-monitor DPI support on Windows

On Windows, Sublime 3143's support for HiDPI is limited to "system" DPI awareness.  If you drag a window to monitor with a differing DPI, the window is bitmap scaled by DWM, resulting in blurry and very unpleasant text rendering.

Sublime should opt-in to per-monitor DPI awareness V2 and handle rescaling a window when it gets WM_DPICHANGE.