New cpp folder structure

Signed-off-by: Alexander Borsuk <me@alex.bio>

libs/shaders/Metal/debug_rect.metal

@@ -0,0 +1,31 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+using namespace metal;
+
+typedef struct
+{
+  float2 a_position [[attribute(0)]];
+} Vertex_T;
+
+typedef struct
+{
+  float4 position [[position]];
+} Fragment_T;
+
+typedef struct
+{
+  float4 u_color;
+} Uniforms_T;
+
+vertex Fragment_T vsDebugRect(const Vertex_T in [[stage_in]])
+{
+  Fragment_T out;
+  out.position = float4(in.a_position, 0.0, 1.0);
+  return out;
+}
+
+fragment float4 fsDebugRect(const Fragment_T in [[stage_in]],
+                            constant Uniforms_T & uniforms [[buffer(0)]])
+{
+  return uniforms.u_color;
+}