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/shadowmappingcascade/depthpass.frag

@@ -0,0 +1,12 @@
+// Copyright 2020 Google LLC
+
+Texture2D colorMapTexture : register(t0, space1);
+SamplerState colorMapSampler : register(s0, space1);
+
+void main([[vk::location(0)]] float2 inUV : TEXCOORD0)
+{
+	float alpha = colorMapTexture.Sample(colorMapSampler, inUV).a;
+	if (alpha < 0.5) {
+		clip(-1);
+	}
+}