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/gpui/examples/image/image.rs

@@ -80,8 +80,8 @@ fn main() {
             }),
 
             window_bounds: Some(WindowBounds::Windowed(Bounds {
-                size: size(px(1100.), px(600.)).into(),
-                origin: Point::new(DevicePixels::from(200), DevicePixels::from(200)),
+                size: size(px(1100.), px(600.)),
+                origin: Point::new(px(200.), px(200.)),
             })),
 
             ..Default::default()

crates/gpui/examples/window_positioning.rs

@@ -24,21 +24,18 @@ fn main() {
 
         for screen in cx.displays() {
             let options = {
-                let popup_margin_width = DevicePixels::from(16);
-                let popup_margin_height = DevicePixels::from(-0) - DevicePixels::from(48);
+                let margin_right = px(16.);
+                let margin_height = px(-48.);
 
-                let window_size = Size {
+                let size = Size {
                     width: px(400.),
                     height: px(72.),
                 };
 
-                let screen_bounds = screen.bounds();
-                let size: Size<DevicePixels> = window_size.into();
-
-                let bounds = gpui::Bounds::<DevicePixels> {
-                    origin: screen_bounds.upper_right()
-                        - point(size.width + popup_margin_width, popup_margin_height),
-                    size: window_size.into(),
+                let bounds = gpui::Bounds::<Pixels> {
+                    origin: screen.bounds().upper_right()
+                        - point(size.width + margin_right, margin_height),
+                    size,
                 };
 
                 WindowOptions {