Align offset to 512 when writing into depth stencil textures on some platforms

On the D3D12 platforms that don't support programmable sample positions,
the source box specifying a portion of the depth texture must all be 0,
or an error and a device lost will occur. This patch adds a workaround
for this issue by alignning the offset of internal staging buffer to 512
when calling Queue.WriteTexture() with depth stencil textures

Bug: dawn:727
Test: dawn_end2end_tests
Change-Id: I6bc5843d62d0aec3964ee5b544a06c0b2657031a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/98601
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

src/dawn/native/Device.cpp

@@ -1928,4 +1928,10 @@ bool DeviceBase::ShouldDuplicateParametersForDrawIndirect(
     return false;
 }
 
+uint64_t DeviceBase::GetBufferCopyOffsetAlignmentForDepthStencil() const {
+    // For depth-stencil texture, buffer offset must be a multiple of 4, which is required
+    // by WebGPU and Vulkan SPEC.
+    return 4u;
+}
+
 }  // namespace dawn::native