Update vertex index decoration names.

This Cl updates the `vertex_idx` to the new `vertex_index` decoration
name.

Change-Id: Ic3688e1af87ed0d570b00ccb72d0e84ac920831b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/38142
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Auto-Submit: dan sinclair <dsinclair@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/examples/ManualSwapChainTest.cpp b/examples/ManualSwapChainTest.cpp
index a9ee509..83ba313 100644
--- a/examples/ManualSwapChainTest.cpp
+++ b/examples/ManualSwapChainTest.cpp
@@ -313,7 +313,7 @@
     // The hacky pipeline to render a triangle.
     utils::ComboRenderPipelineDescriptor pipelineDesc(device);
     pipelineDesc.vertexStage.module = utils::CreateShaderModuleFromWGSL(device, R"(
-        [[builtin(vertex_idx)]] var<in> VertexIndex : u32;
+        [[builtin(vertex_index)]] var<in> VertexIndex : u32;
         [[builtin(position)]] var<out> Position : vec4<f32>;
         const pos : array<vec2<f32>, 3> = array<vec2<f32>, 3>(
             vec2<f32>( 0.0,  0.5),