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/computenbody/particle_integrate.comp

@@ -0,0 +1,28 @@
+// Copyright 2020 Google LLC
+
+struct Particle
+{
+	float4 pos;
+	float4 vel;
+};
+
+// Binding 0 : Position storage buffer
+RWStructuredBuffer<Particle> particles : register(u0);
+
+struct UBO
+{
+	float deltaT;
+	int particleCount;
+};
+
+cbuffer ubo : register(b1) { UBO ubo; }
+
+[numthreads(256, 1, 1)]
+void main(uint3 GlobalInvocationID : SV_DispatchThreadID)
+{
+	int index = int(GlobalInvocationID.x);
+	float4 position = particles[index].pos;
+	float4 velocity = particles[index].vel;
+	position += ubo.deltaT * velocity;
+	particles[index].pos = position;
+}