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/deferredmultisampling/debug.frag

@@ -0,0 +1,53 @@
+// Copyright 2020 Google LLC
+
+Texture2DMS<float4> texturePosition : register(t1);
+SamplerState samplerPosition : register(s1);
+Texture2DMS<float4> textureNormal : register(t2);
+SamplerState samplerNormal : register(s2);
+Texture2DMS<float4> textureAlbedo : register(t3);
+SamplerState samplerAlbedo : register(s3);
+
+[[vk::constant_id(0)]] const int NUM_SAMPLES = 8;
+
+float4 resolve(Texture2DMS<float4> tex, int2 uv)
+{
+	float4 result = float4(0.0, 0.0, 0.0, 0.0);
+	int count = 0;
+	for (int i = 0; i < NUM_SAMPLES; i++)
+	{
+		uint status = 0;
+		float4 val = tex.Load(uv, i, int2(0, 0), status);
+		result += val;
+		count++;
+	}
+	return result / float(NUM_SAMPLES);
+}
+
+float4 main([[vk::location(0)]] float3 inUV : TEXCOORD0) : SV_TARGET
+{
+	int2 attDim; int sampleCount;
+	texturePosition.GetDimensions(attDim.x, attDim.y, sampleCount);
+	int2 UV = int2(inUV.xy * attDim * 2.0);
+
+	int index = 0;
+	if (inUV.x > 0.5)
+	{
+		index = 1;
+		UV.x -= attDim.x;
+	}
+	if (inUV.y > 0.5)
+	{
+		index = 2;
+		UV.y -= attDim.y;
+	}
+
+	float3 components[3];
+	components[0] = resolve(texturePosition, UV).rgb;
+	components[1] = resolve(textureNormal, UV).rgb;
+	components[2] = resolve(textureAlbedo, UV).rgb;
+	// Uncomment to display specular component
+	//components[2] = float3(textureAlbedo.Sample(samplerAlbedo, inUV.xt).a);
+
+	// Select component depending on UV
+	return float4(components[index], 1);
+}