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/shadowmapping/offscreen.vert

@@ -0,0 +1,13 @@
+// Copyright 2020 Google LLC
+
+struct UBO
+{
+	float4x4 depthMVP;
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+float4 main([[vk::location(0)]] float3 Pos : POSITION0) : SV_POSITION
+{
+	return mul(ubo.depthMVP, float4(Pos, 1.0));
+}