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/shadowmappingcascade/debugshadowmap.vert

@@ -0,0 +1,23 @@
+// Copyright 2020 Google LLC
+
+struct PushConsts {
+	float4 position;
+	uint cascadeIndex;
+};
+[[vk::push_constant]] PushConsts pushConsts;
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float2 UV : TEXCOORD0;
+[[vk::location(1)]] uint CascadeIndex : TEXCOORD1;
+};
+
+VSOutput main(uint VertexIndex : SV_VertexID)
+{
+	VSOutput output = (VSOutput)0;
+	output.UV = float2((VertexIndex << 1) & 2, VertexIndex & 2);
+	output.CascadeIndex = pushConsts.cascadeIndex;
+	output.Pos = float4(output.UV * 2.0f - 1.0f, 0.0f, 1.0f);
+	return output;
+}