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

---------

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

crates/editor/src/editor_tests.rs

@@ -7659,8 +7659,8 @@ async fn test_following(cx: &mut gpui::TestAppContext) {
         cx.open_window(
             WindowOptions {
                 window_bounds: Some(WindowBounds::Windowed(Bounds::from_corners(
-                    gpui::Point::new(0.into(), 0.into()),
-                    gpui::Point::new(10.into(), 80.into()),
+                    gpui::Point::new(px(0.), px(0.)),
+                    gpui::Point::new(px(10.), px(80.)),
                 ))),
                 ..Default::default()
             },