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/computeparticles/particle.frag

@@ -0,0 +1,22 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureColorMap : register(t0);
+SamplerState samplerColorMap : register(s0);
+Texture2D textureGradientRamp : register(t1);
+SamplerState samplerGradientRamp : register(s1);
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float4 Color : COLOR0;
+[[vk::location(1)]] float GradientPos : POSITION0;
+[[vk::location(2)]] float2 CenterPos : POSITION1;
+[[vk::location(3)]] float PointSize : TEXCOORD0;
+};
+
+float4 main (VSOutput input) : SV_TARGET
+{
+	float3 color = textureGradientRamp.Sample(samplerGradientRamp, float2(input.GradientPos, 0.0)).rgb;
+	float2 PointCoord = (input.Pos.xy - input.CenterPos.xy) / input.PointSize + 0.5;
+	return float4(textureColorMap.Sample(samplerColorMap, PointCoord).rgb * color, 1.0);
+}