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/glsl/subpasses/transparent.frag

@@ -0,0 +1,34 @@
+#version 450
+
+layout (input_attachment_index = 0, binding = 1) uniform subpassInput samplerPositionDepth;
+layout (binding = 2) uniform sampler2D samplerTexture;
+
+layout (location = 0) in vec3 inColor;
+layout (location = 1) in vec2 inUV;
+
+layout (location = 0) out vec4 outColor;
+
+layout (constant_id = 0) const float NEAR_PLANE = 0.1f;
+layout (constant_id = 1) const float FAR_PLANE = 256.0f;
+
+float linearDepth(float depth)
+{
+	float z = depth * 2.0f - 1.0f; 
+	return (2.0f * NEAR_PLANE * FAR_PLANE) / (FAR_PLANE + NEAR_PLANE - z * (FAR_PLANE - NEAR_PLANE));	
+}
+
+void main () 
+{
+	// Sample depth from deferred depth buffer and discard if obscured
+	float depth = subpassLoad(samplerPositionDepth).a;
+
+	// Save the sampled texture color before discarding.
+	// This is to avoid implicit derivatives in non-uniform control flow.
+	vec4 sampledColor = texture(samplerTexture, inUV);
+	if ((depth != 0.0) && (linearDepth(gl_FragCoord.z) > depth))
+	{
+		discard;
+	};
+
+	outColor = sampledColor;
+}