Use C++17 [[nodiscard]] and [[fallthrough]] attributes

Bug: dawn:824
Change-Id: Ied4f2eb736e0c3488a79e4872e7ffa3eb2fdaac5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/75063
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn_wire/WireResult.h

@@ -19,7 +19,7 @@
 
 namespace dawn_wire {
 
-    enum class DAWN_NO_DISCARD WireResult {
+    enum class [[nodiscard]] WireResult{
         Success,
         FatalError,
     };