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/gbuffer.frag

@@ -0,0 +1,45 @@
+// Copyright 2020 Google LLC
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 WorldPos : POSITION0;
+};
+
+struct FSOutput
+{
+[[vk::location(0)]] float4 Color : SV_TARGET0;
+[[vk::location(1)]] float4 Position : SV_TARGET1;
+[[vk::location(2)]] float4 Normal : SV_TARGET2;
+[[vk::location(3)]] float4 Albedo : SV_TARGET3;
+};
+
+[[vk::constant_id(0)]] const float NEAR_PLANE = 0.1f;
+[[vk::constant_id(1)]] const float FAR_PLANE = 256.0f;
+
+float linearDepth(float depth)
+{
+	float z = depth * 2.0f - 1.0f;
+	return (2.0f * NEAR_PLANE * FAR_PLANE) / (FAR_PLANE + NEAR_PLANE - z * (FAR_PLANE - NEAR_PLANE));
+}
+
+FSOutput main(VSOutput input)
+{
+	FSOutput output = (FSOutput)0;
+	output.Position = float4(input.WorldPos, 1.0);
+
+	float3 N = normalize(input.Normal);
+	N.y = -N.y;
+	output.Normal = float4(N, 1.0);
+
+	output.Albedo.rgb = input.Color;
+
+	// Store linearized depth in alpha component
+	output.Position.a = linearDepth(input.Pos.z);
+
+	// Write color attachments to avoid undefined behaviour (validation error)
+	output.Color = float4(0.0, 0.0, 0.0, 0.0);
+	return output;
+}