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/computeshader/emboss.comp

@@ -0,0 +1,40 @@
+// Copyright 2020 Google LLC
+
+Texture2D inputImage : register(t0);
+RWTexture2D<float4> resultImage : register(u1);
+
+float conv(in float kernel[9], in float data[9], in float denom, in float offset)
+{
+   float res = 0.0;
+   for (int i=0; i<9; ++i)
+   {
+      res += kernel[i] * data[i];
+   }
+   return saturate(res/denom + offset);
+}
+
+[numthreads(16, 16, 1)]
+void main(uint3 GlobalInvocationID : SV_DispatchThreadID)
+{
+	float imageData[9];
+	// Fetch neighbouring texels
+	int n = -1;
+	for (int i=-1; i<2; ++i)
+	{
+		for(int j=-1; j<2; ++j)
+		{
+			n++;
+			float3 rgb = inputImage[uint2(GlobalInvocationID.x + i, GlobalInvocationID.y + j)].rgb;
+			imageData[n] = (rgb.r + rgb.g + rgb.b) / 3.0;
+		}
+	}
+
+	float kernel[9];
+	kernel[0] = -1.0; kernel[1] =  0.0; kernel[2] =  0.0;
+	kernel[3] = 0.0; kernel[4] = -1.0; kernel[5] =  0.0;
+	kernel[6] = 0.0; kernel[7] =  0.0; kernel[8] = 2.0;
+
+	float4 res = float4(conv(kernel, imageData, 1.0, 0.50).xxx, 1.0);
+
+	resultImage[int2(GlobalInvocationID.xy)] = res;
+}