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/texturecubemap/skybox.vert

@@ -0,0 +1,25 @@
+// Copyright 2020 Google LLC
+
+struct UBO
+{
+	float4x4 projection;
+	float4x4 view;
+	float4x4 model;
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 UVW : TEXCOORD0;
+};
+
+VSOutput main([[vk::location(0)]] float3 Pos : POSITION0)
+{
+	VSOutput output = (VSOutput)0;
+	output.UVW = Pos;
+	output.UVW.x *= -1.0;
+	output.Pos = mul(ubo.projection, mul(ubo.view, mul(ubo.model, float4(Pos.xyz, 1.0))));
+	return output;
+}