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/indirectdraw/skysphere.frag

@@ -0,0 +1,11 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureColor : register(t2);
+SamplerState samplerColor : register(s2);
+
+float4 main([[vk::location(0)]] float2 inUV : TEXCOORD0) : SV_TARGET
+{
+	const float4 gradientStart = float4(0.93, 0.9, 0.81, 1.0);
+	const float4 gradientEnd = float4(0.35, 0.5, 1.0, 1.0);
+	return lerp(gradientStart, gradientEnd, min(0.5 - inUV.y, 0.5)/0.15 + 0.5);
+}