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/multithreading/starsphere.vert

@@ -0,0 +1,21 @@
+// Copyright 2020 Google LLC
+
+struct PushConsts
+{
+	float4x4 mvp;
+};
+[[vk::push_constant]]PushConsts pushConsts;
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 UVW : TEXCOORD0;
+};
+
+VSOutput main([[vk::location(0)]] float3 Pos : POSITION0)
+{
+	VSOutput output = (VSOutput)0;
+	output.UVW = Pos;
+	output.Pos = mul(pushConsts.mvp, float4(Pos.xyz, 1.0));
+	return output;
+}