Rename DeviceDescriptor -> DawnDeviceDescriptor

This is preventing supporting DeviceDescriptor from upstream
webgpu.h because the name conflicts with the existing struct.

A typedef using the original name DeviceDescriptor is added
until all embedders of Dawn are updated to use the new name.

Bug: dawn:160, dawn:689
Change-Id: Ib9cb7443b7e46e3ffe29d2ec109f2f1a831754e7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/70581
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/tests/unittests/validation/TextureValidationTests.cpp

@@ -586,7 +586,7 @@ namespace {
     class CompressedTextureFormatsValidationTests : public TextureValidationTest {
       protected:
         WGPUDevice CreateTestDevice() override {
-            dawn_native::DeviceDescriptor descriptor;
+            dawn_native::DawnDeviceDescriptor descriptor;
             descriptor.requiredFeatures = {"texture-compression-bc", "texture-compression-etc2",
                                            "texture-compression-astc"};
             return adapter.CreateDevice(&descriptor);