Move shaders into glsl and hlsl directories

Move `data/shaders` to `data/shaders/glsl`
Move `data/hlsl` to `data/shaders/hlsl`

Fix up shader paths in the cpp files to point to the new glsl location.

`data/shaders/hlsl/compile.py` still overwrites the glsl .spv files (for
now).

Issue: #723

data/shaders/hlsl/deferredshadows/debug.frag

@@ -0,0 +1,26 @@
+// Copyright 2020 Google LLC
+
+Texture2D texturePosition : register(t1);
+SamplerState samplerPosition : register(s1);
+Texture2D textureNormal : register(t2);
+SamplerState samplerNormal : register(s2);
+Texture2D textureAlbedo : register(t3);
+SamplerState samplerAlbedo : register(s3);
+Texture2DArray textureDepth : register(t5);
+SamplerState samplerDepth : register(s5);
+
+float LinearizeDepth(float depth)
+{
+  float n = 0.1; // camera z near
+  float f = 64.0; // camera z far
+  float z = depth;
+  return (2.0 * n) / (f + n - z * (f - n));
+}
+
+float4 main([[vk::location(0)]] float3 inUV : TEXCOORD0) : SV_TARGET
+{
+	// Display depth from light's point-of-view
+	// inUV.w = number of light source
+	float depth = textureDepth.Sample(samplerDepth, float3(inUV)).r;
+	return float4((1.0 - LinearizeDepth(depth)).xxx, 0.0);
+}