Make shim headers at <webgpu/*> that point to <dawn/*>

Emscripten's headers live at <webgpu/*>; this makes it so projects don't
have to ifdef which #include path to use.

Bug: dawn:160
Change-Id: I39efee44447470551a78db0abd062f4a2fe9083a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/26020
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/include/webgpu/webgpu.h b/src/include/webgpu/webgpu.h
new file mode 100644
index 0000000..4a29d37
--- /dev/null
+++ b/src/include/webgpu/webgpu.h
@@ -0,0 +1 @@
+#include "dawn/webgpu.h"
diff --git a/src/include/webgpu/webgpu_cpp.h b/src/include/webgpu/webgpu_cpp.h
new file mode 100644
index 0000000..5bbd869
--- /dev/null
+++ b/src/include/webgpu/webgpu_cpp.h
@@ -0,0 +1 @@
+#include <dawn/webgpu_cpp.h>