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/gears/gears.frag

@@ -0,0 +1,22 @@
+// Copyright 2020 Google LLC
+
+struct VSOutput
+{
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 EyePos : POSITION0;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+};
+
+float4 main(VSOutput input) : SV_TARGET
+{
+  float3 Eye = normalize(-input.EyePos);
+  float3 Reflected = normalize(reflect(-input.LightVec, input.Normal));
+
+  float4 IAmbient = float4(0.2, 0.2, 0.2, 1.0);
+  float4 IDiffuse = float4(0.5, 0.5, 0.5, 0.5) * max(dot(input.Normal, input.LightVec), 0.0);
+  float specular = 0.25;
+  float4 ISpecular = float4(0.5, 0.5, 0.5, 1.0) * pow(max(dot(Reflected, Eye), 0.0), 0.8) * specular;
+
+  return float4((IAmbient + IDiffuse) * float4(input.Color, 1.0) + ISpecular);
+}

data/shaders/hlsl/gears/gears.vert

@@ -0,0 +1,42 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float4 Pos : POSITION0;
+[[vk::location(1)]] float3 Normal : NORMAL0;
+[[vk::location(2)]] float3 Color : COLOR0;
+};
+
+struct UBO
+{
+	float4x4 projection;
+	float4x4 model;
+	float4x4 normal;
+	float4x4 view;
+	float3 lightpos;
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 EyePos : POSITION0;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+};
+
+VSOutput main(VSInput input)
+{
+	VSOutput output = (VSOutput)0;
+	output.Normal = normalize(mul((float4x3)ubo.normal, input.Normal).xyz);
+	output.Color = input.Color;
+	float4x4 modelView = mul(ubo.view, ubo.model);
+	float4 pos = mul(modelView, input.Pos);
+	output.EyePos = mul(modelView, pos).xyz;
+	float4 lightPos = mul(float4(ubo.lightpos, 1.0), modelView);
+	output.LightVec = normalize(lightPos.xyz - output.EyePos);
+	output.Pos = mul(ubo.projection, pos);
+	return output;
+}