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/hdr/composition.frag

@@ -0,0 +1,11 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureColor0 : register(t0);
+SamplerState samplerColor0 : register(s0);
+Texture2D textureColor1 : register(t1);
+SamplerState samplerColor1 : register(s1);
+
+float4 main([[vk::location(0)]] float2 inUV : TEXCOORD0) : SV_TARGET
+{
+	return textureColor0.Sample(samplerColor0, inUV);
+}