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/multiview/multiview.vert

@@ -0,0 +1,43 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float3 Pos : POSITION0;
+[[vk::location(1)]] float3 Normal : NORMAL0;
+[[vk::location(2)]] float3 Color : COLOR0;
+};
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 ViewVec : TEXCOORD1;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+};
+
+struct UBO
+{
+	float4x4 projection[2];
+	float4x4 modelview[2];
+	float4 lightPos;
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+VSOutput main(VSInput input, uint ViewIndex : SV_ViewID)
+{
+	VSOutput output = (VSOutput)0;
+	output.Color = input.Color;
+	output.Normal = mul((float3x3)ubo.modelview[ViewIndex], input.Normal);
+
+	float4 pos = float4(input.Pos.xyz, 1.0);
+	float4 worldPos = mul(ubo.modelview[ViewIndex], pos);
+
+	float3 lPos = mul(ubo.modelview[ViewIndex], ubo.lightPos).xyz;
+	output.LightVec = lPos - worldPos.xyz;
+	output.ViewVec = -worldPos.xyz;
+
+	output.Pos = mul(ubo.projection[ViewIndex], worldPos);
+	return output;
+}