Rename STRIDE_UNDEFINED to COPY_STRIDE_UNDEFINED

Per https://github.com/webgpu-native/webgpu-headers/pull/71

Keeps but deprecates WGPU_STRIDE_UNDEFINED/wgpu::kStrideUndefined.

Bug: dawn:520
Change-Id: Ied162ec39454fac3d16a3782c9ed6d2f68c1d41d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/34926
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Kai Ninomiya <kainino@chromium.org>

src/dawn_platform/DawnPlatform.cpp

@@ -55,4 +55,4 @@ namespace dawn_platform {
         return nullptr;
     }
 
-}  // namespace dawn_platform
+}  // namespace dawn_platform