gpui: Rename GPUSpecs to GpuSpecs (#22166)

This PR renames the `GPUSpecs` type to `GpuSpecs` to match Rust naming
conventions.

Release Notes:

- N/A

crates/gpui/src/platform/test/window.rs

@@ -1,5 +1,5 @@
 use crate::{
-    AnyWindowHandle, AtlasKey, AtlasTextureId, AtlasTile, Bounds, DispatchEventResult, GPUSpecs,
+    AnyWindowHandle, AtlasKey, AtlasTextureId, AtlasTile, Bounds, DispatchEventResult, GpuSpecs,
     Pixels, PlatformAtlas, PlatformDisplay, PlatformInput, PlatformInputHandler, PlatformWindow,
     Point, RequestFrameOptions, ScaledPixels, Size, TestPlatform, TileId, WindowAppearance,
     WindowBackgroundAppearance, WindowBounds, WindowParams,
@@ -276,7 +276,7 @@ impl PlatformWindow for TestWindow {
 
     fn update_ime_position(&self, _bounds: Bounds<ScaledPixels>) {}
 
-    fn gpu_specs(&self) -> Option<GPUSpecs> {
+    fn gpu_specs(&self) -> Option<GpuSpecs> {
         None
     }
 }