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/renderheadless/triangle.frag

@@ -0,0 +1,6 @@
+// Copyright 2020 Google LLC
+
+float4 main([[vk::location(0)]] float3 Color : COLOR0) : SV_TARGET
+{
+  return float4(Color, 1.0);
+}

data/hlsl/renderheadless/triangle.vert

@@ -0,0 +1,26 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float3 Pos : POSITION0;
+[[vk::location(1)]] float3 Color : COLOR0;
+};
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 Color : COLOR0;
+};
+
+struct PushConsts {
+	float4x4 mvp;
+};
+[[vk::push_constant]] PushConsts pushConsts;
+
+VSOutput main(VSInput input)
+{
+	VSOutput output = (VSOutput)0;
+	output.Color = input.Color;
+	output.Pos = mul(pushConsts.mvp, float4(input.Pos.xyz, 1.0));
+	return output;
+}