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_shadows/shadow.rmiss

@@ -0,0 +1,7 @@
+// Copyright 2020 Google LLC
+
+[shader("miss")]
+void main([[vk::location(2)]] in bool shadowed)
+{
+	shadowed = false;
+}