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/deferredshadows/shadow.geom

@@ -0,0 +1,39 @@
+// Copyright 2020 Google LLC
+
+#define LIGHT_COUNT 3
+
+struct UBO
+{
+	float4x4 mvp[LIGHT_COUNT];
+	float4 instancePos[3];
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] int InstanceIndex : TEXCOORD0;
+};
+
+struct GSOutput
+{
+	float4 Pos : SV_POSITION;
+	int Layer : SV_RenderTargetArrayIndex;
+};
+
+[maxvertexcount(3)]
+[instance(3)]
+void main(triangle VSOutput input[3], uint InvocationID : SV_GSInstanceID, inout TriangleStream<GSOutput> outStream)
+{
+	float4 instancedPos = ubo.instancePos[input[0].InstanceIndex];
+	for (int i = 0; i < 3; i++)
+	{
+		float4 tmpPos = input[i].Pos + instancedPos;
+		GSOutput output = (GSOutput)0;
+		output.Pos = mul(ubo.mvp[InvocationID], tmpPos);
+		output.Layer = InvocationID;
+		outStream.Append( output );
+	}
+	outStream.RestartStrip();
+}