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/depthpass.vert

@@ -0,0 +1,36 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float3 Pos : POSITION0;
+[[vk::location(1)]] float2 UV : TEXCOORD0;
+};
+// todo: pass via specialization constant
+#define SHADOW_MAP_CASCADE_COUNT 4
+
+struct PushConsts {
+	float4 position;
+	uint cascadeIndex;
+};
+[[vk::push_constant]] PushConsts pushConsts;
+
+struct UBO  {
+	float4x4 cascadeViewProjMat[SHADOW_MAP_CASCADE_COUNT];
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float2 UV : TEXCOORD0;
+};
+
+VSOutput main(VSInput input)
+{
+	VSOutput output = (VSOutput)0;
+	output.UV = input.UV;
+	float3 pos = input.Pos + pushConsts.position.xyz;
+	output.Pos = mul(ubo.cascadeViewProjMat[pushConsts.cascadeIndex], float4(pos, 1.0));
+	return output;
+}