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/offscreen/mirror.frag

@@ -0,0 +1,38 @@
+#version 450
+
+layout (binding = 1) uniform sampler2D samplerColor;
+
+layout (location = 0) in vec2 inUV;
+layout (location = 1) in vec4 inPos;
+
+layout (location = 0) out vec4 outFragColor;
+
+void main() 
+{
+	vec4 tmp = vec4(1.0 / inPos.w);
+	vec4 projCoord = inPos * tmp;
+
+	// Scale and bias
+	projCoord += vec4(1.0);
+	projCoord *= vec4(0.5);
+		
+	// Slow single pass blur
+	// For demonstration purposes only
+	const float blurSize = 1.0 / 512.0;	
+
+	outFragColor = vec4(vec3(0.0), 1.);
+
+	if (gl_FrontFacing) 
+	{
+		// Only render mirrored scene on front facing (upper) side of mirror surface
+		vec4 reflection = vec4(0.0);
+		for (int x = -3; x <= 3; x++)
+		{
+			for (int y = -3; y <= 3; y++)
+			{
+				reflection += texture(samplerColor, vec2(projCoord.s + x * blurSize, projCoord.t + y * blurSize)) / 49.0;
+			}
+		}
+		outFragColor += reflection;
+	};
+}