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/texturearray/instancing.frag

@@ -0,0 +1,9 @@
+// Copyright 2020 Google LLC
+
+Texture2DArray textureArray : register(t1);
+SamplerState samplerArray : register(s1);
+
+float4 main([[vk::location(0)]] float3 inUV : TEXCOORD0) : SV_TARGET
+{
+	return textureArray.Sample(samplerArray, inUV);
+}