gpui: Fix pre-edit position after applying scale factor (#18214)

before:

![image](https://github.com/user-attachments/assets/20590089-3333-4ca8-a371-b07acfbe43f9)

after:

![image](https://github.com/user-attachments/assets/2d25623e-0602-4d24-b563-64e1d2ec3492)

Release Notes:

- N/A

crates/gpui/src/geometry.rs

@@ -2612,6 +2612,12 @@ impl From<ScaledPixels> for f64 {
     }
 }
 
+impl From<ScaledPixels> for u32 {
+    fn from(pixels: ScaledPixels) -> Self {
+        pixels.0 as u32
+    }
+}
+
 /// Represents a length in rems, a unit based on the font-size of the window, which can be assigned with [`WindowContext::set_rem_size`][set_rem_size].
 ///
 /// Rems are used for defining lengths that are scalable and consistent across different UI elements.