Add sampling helpers

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Resources/CombineSubsurfaceScattering.shader

             {                                                                                   \
                 float  r   = kernel[profileID][i][0];                                           \
                 /* The relative sample position is known at compile time. */                    \
-                float  phi = TWO_PI * Fibonacci2d(i, n).y;                                      \
+                float  phi = SampleDiskFibonacci(i, n).y;                                       \
                 float2 vec = r * float2(cos(phi), sin(phi));                                    \
                                                                                                 \
                 /* Compute the screen-space position and the associated irradiance. */          \

Assets/ScriptableRenderPipeline/ShaderLibrary/Fibonacci.hlsl

     }
 }
 
+// Returns the radius as the X coordinate, and the angle as the Y coordinate.
+float2 SampleDiskFibonacci(uint i, uint sampleCount)
+{
+    float2 f = Fibonacci2d(i, sampleCount);
+    return float2(f.x, TWO_PI * f.y);
+}
+
+// Returns the zenith as the X coordinate, and the azimuthal angle as the Y coordinate.
+float2 SampleHemisphereFibonacci(uint i, uint sampleCount)
+{
+    float2 f = Fibonacci2d(i, sampleCount);
+    return float2(1 - f.x, TWO_PI * f.y);
+}
+
+// Returns the zenith as the X coordinate, and the azimuthal angle as the Y coordinate.
+float2 SampleSphereFibonacci(uint i, uint sampleCount)
+{
+    float2 f = Fibonacci2d(i, sampleCount);
+    return float2(1 - 2 * f.x, TWO_PI * f.y);
+}
+
 #endif // UNITY_FIBONACCI_INCLUDED