Change canvas/context/snapshot size from u64 -> u32 (#36827)

Replaces uses of `euclid::default::Size2D<u64>` with
`euclid::default::Size2D<u32>` for the canvas/context/snapshot.

This PR includes changes to the following components:
 - canvas
 - pixels
 - script
 - script_bindings
 - shared/canvas
 - shared/snapshot

Testing: https://github.com/hashcatHitman/servo/actions/runs/15426115391
(as of 892edc0048)

Fixes: #36706

---------

Signed-off-by: hashcatHitman <155700084+hashcatHitman@users.noreply.github.com>

components/script/dom/webgpu/gpucanvascontext.rs

@@ -167,8 +167,8 @@ impl GPUCanvasContext {
             // causes FAIL on webgpu:web_platform,canvas,configure:usage:*
             usage: configuration.usage | GPUTextureUsageConstants::COPY_SRC,
             size: GPUExtent3D::GPUExtent3DDict(GPUExtent3DDict {
-                width: size.width as u32,
-                height: size.height as u32,
+                width: size.width,
+                height: size.height,
                 depthOrArrayLayers: 1,
             }),
             viewFormats: configuration.viewFormats.clone(),