Fix issues where screen and window sizes contained Pixels, but were declared as DevicePixels (#12991)

On most platforms, things were working correctly, but had the wrong
type. On X11, there were some problems with window and display size
calculations.

Release Notes:

- Fixed issues with window positioning on X11

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Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: Mikayla <mikayla@zed.dev>