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/subpasses/composition.frag

@@ -0,0 +1,69 @@
+// Copyright 2020 Google LLC
+
+[[vk::input_attachment_index(0)]][[vk::binding(0)]] SubpassInput samplerposition;
+[[vk::input_attachment_index(1)]][[vk::binding(1)]] SubpassInput samplerNormal;
+[[vk::input_attachment_index(2)]][[vk::binding(2)]] SubpassInput samplerAlbedo;
+
+#define MAX_NUM_LIGHTS 64
+[[vk::constant_id(0)]] const int NUM_LIGHTS = 64;
+
+struct Light {
+	float4 position;
+	float3 color;
+	float radius;
+};
+
+struct UBO
+{
+	float4 viewPos;
+	Light lights[MAX_NUM_LIGHTS];
+};
+
+cbuffer ubo : register(b3) { UBO ubo; }
+
+
+float4 main([[vk::location(0)]] float2 inUV : TEXCOORD) : SV_TARGET
+{
+	// Read G-Buffer values from previous sub pass
+	float3 fragPos = samplerposition.SubpassLoad().rgb;
+	float3 normal = samplerNormal.SubpassLoad().rgb;
+	float4 albedo = samplerAlbedo.SubpassLoad();
+
+	#define ambient 0.15
+
+	// Ambient part
+	float3 fragcolor  = albedo.rgb * ambient;
+
+	for(int i = 0; i < NUM_LIGHTS; ++i)
+	{
+		// Vector to light
+		float3 L = ubo.lights[i].position.xyz - fragPos;
+		// Distance from light to fragment position
+		float dist = length(L);
+
+		// Viewer to fragment
+		float3 V = ubo.viewPos.xyz - fragPos;
+		V = normalize(V);
+
+		// Light to fragment
+		L = normalize(L);
+
+		// Attenuation
+		float atten = ubo.lights[i].radius / (pow(dist, 2.0) + 1.0);
+
+		// Diffuse part
+		float3 N = normalize(normal);
+		float NdotL = max(0.0, dot(N, L));
+		float3 diff = ubo.lights[i].color * albedo.rgb * NdotL * atten;
+
+		// Specular part
+		// Specular map values are stored in alpha of albedo mrt
+		float3 R = reflect(-L, N);
+		float NdotR = max(0.0, dot(R, V));
+		//float3 spec = ubo.lights[i].color * albedo.a * pow(NdotR, 32.0) * atten;
+
+		fragcolor += diff;// + spec;
+	}
+
+	return float4(fragcolor, 1.0);
+}