Add shaders re-implemented in HLSL

These were written against the shaders at revision eddd724e7.
There have been changes made since then, which will need to be mirrored.

See `data/hlsl/README.md` for the current status of each sample.

data/hlsl/nv_ray_tracing_basic/closesthit.rchit

@@ -0,0 +1,18 @@
+// Copyright 2020 Google LLC
+
+struct Attribute
+{
+  float2 attribs;
+};
+
+struct Payload
+{
+[[vk::location(0)]] float3 hitValue;
+};
+
+[shader("closesthit")]
+void main(inout Payload p, in float3 attribs)
+{
+  const float3 barycentricCoords = float3(1.0f - attribs.x - attribs.y, attribs.x, attribs.y);
+  p.hitValue = barycentricCoords;
+}