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_reflections/raygen.rgen

@@ -0,0 +1,64 @@
+// Copyright 2020 Google LLC
+
+RaytracingAccelerationStructure rs : register(t0);
+RWTexture2D<float4> image : register(u1);
+
+struct CameraProperties
+{
+	float4x4 viewInverse;
+	float4x4 projInverse;
+	float4 lightPos;
+};
+cbuffer cam : register(b2) { CameraProperties cam; };
+
+
+struct RayPayload {
+	float3 color;
+	float distance;
+	float3 normal;
+	float reflector;
+};
+
+// Max. number of recursion is passed via a specialization constant
+[[vk::constant_id(0)]] const int MAX_RECURSION = 0;
+
+[shader("raygeneration")]
+void main()
+{
+	uint3 LaunchID = DispatchRaysIndex();
+	uint3 LaunchSize = DispatchRaysDimensions();
+
+	const float2 pixelCenter = float2(LaunchID.xy) + float2(0.5, 0.5);
+	const float2 inUV = pixelCenter/float2(LaunchSize.xy);
+	float2 d = inUV * 2.0 - 1.0;
+	float4 target = mul(cam.projInverse, float4(d.x, d.y, 1, 1));
+
+	RayDesc rayDesc;
+	rayDesc.Origin = mul(cam.viewInverse, float4(0,0,0,1)).xyz;
+	rayDesc.Direction = mul(cam.viewInverse, float4(normalize(target.xyz), 0)).xyz;
+	rayDesc.TMin = 0.001;
+	rayDesc.TMax = 10000.0;
+
+	float3 color = float3(0.0, 0.0, 0.0);
+
+	for (int i = 0; i < MAX_RECURSION; i++) {
+		RayPayload rayPayload;
+		TraceRay(rs, RAY_FLAG_FORCE_OPAQUE, 0xff, 0, 0, 0, rayDesc, rayPayload);
+		float3 hitColor = rayPayload.color;
+
+		if (rayPayload.distance < 0.0f) {
+			color += hitColor;
+			break;
+		} else if (rayPayload.reflector == 1.0f) {
+			const float3 hitPos = rayDesc.Origin + rayDesc.Direction * rayPayload.distance;
+			rayDesc.Origin = hitPos + rayPayload.normal * 0.001f;
+			rayDesc.Direction = reflect(rayDesc.Direction, rayPayload.normal);
+		} else {
+			color += hitColor;
+			break;
+		}
+
+	}
+
+	image[int2(LaunchID.xy)] = float4(color, 0.0);
+}