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.frag

@@ -0,0 +1,12 @@
+// Copyright 2020 Google LLC
+
+Texture2D colorMapTexture : register(t0, space1);
+SamplerState colorMapSampler : register(s0, space1);
+
+void main([[vk::location(0)]] float2 inUV : TEXCOORD0)
+{
+	float alpha = colorMapTexture.Sample(colorMapSampler, inUV).a;
+	if (alpha < 0.5) {
+		clip(-1);
+	}
+}