Add explicit in include/dawn

This CL adds some explicit notations to single argument constructors in
the include/dawn folder.

Bug: dawn:1339
Change-Id: Ie4e31bf68f920acfcfb27828a465e45fe0977af6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86443
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/dawn/native/DawnNative.cpp

@@ -210,7 +210,7 @@ namespace dawn::native {
         // Adapters are owned by mImpl so it is safe to return non RAII pointers to them
         std::vector<Adapter> adapters;
         for (const Ref<AdapterBase>& adapter : mImpl->GetAdapters()) {
-            adapters.push_back({adapter.Get()});
+            adapters.push_back(Adapter(adapter.Get()));
         }
         return adapters;
     }