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/pipelines/phong.frag

@@ -0,0 +1,29 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureColorMap : register(t1);
+SamplerState samplerColorMap : register(s1);
+
+struct VSOutput
+{
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float2 UV : TEXCOORD0;
+[[vk::location(3)]] float3 ViewVec : TEXCOORD1;
+[[vk::location(4)]] float3 LightVec : TEXCOORD2;
+};
+
+float4 main(VSOutput input) : SV_TARGET
+{
+	// Desaturate color
+    float3 color = lerp(input.Color, dot(float3(0.2126,0.7152,0.0722), input.Color).xxx, 0.65);
+
+	// High ambient colors because mesh materials are pretty dark
+	float3 ambient = color * float3(1.0, 1.0, 1.0);
+	float3 N = normalize(input.Normal);
+	float3 L = normalize(input.LightVec);
+	float3 V = normalize(input.ViewVec);
+	float3 R = reflect(-L, N);
+	float3 diffuse = max(dot(N, L), 0.0) * color;
+	float3 specular = pow(max(dot(R, V), 0.0), 32.0) * float3(0.35, 0.35, 0.35);
+	return float4(ambient + diffuse * 1.75 + specular, 1.0);
+}