Fix fog node preview rendering

- Add Fog parameters and reversed Z calc to graph library

com.unity.shadergraph/ShaderGraphLibrary/ShaderVariables.hlsl

     float4 unity_AmbientEquator;
     float4 unity_AmbientGround;
     float4 unity_IndirectSpecColor;
+    float4 unity_FogParams;
+    half4  unity_FogColor;
 
 #if !defined(USING_STEREO_MATRICES)
     float4x4 glstate_matrix_projection;

com.unity.shadergraph/ShaderGraphLibrary/ShaderVariablesFunctions.hlsl

     projMatrix._13_23_33_43 = -projMatrix._13_23_33_43;
 }
 
+#if UNITY_REVERSED_Z
+    #if SHADER_API_OPENGL || SHADER_API_GLES || SHADER_API_GLES3
+        //GL with reversed z => z clip range is [near, -far] -> should remap in theory but dont do it in practice to save some perf (range is close enough)
+        #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) max(-(coord), 0)
+    #else
+        //D3d with reversed Z => z clip range is [near, 0] -> remapping to [0, far]
+        //max is required to protect ourselves from near plane not being correct/meaningfull in case of oblique matrices.
+        #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) max(((1.0-(coord)/_ProjectionParams.y)*_ProjectionParams.z),0)
+    #endif
+#elif UNITY_UV_STARTS_AT_TOP
+    //D3d without reversed z => z clip range is [0, far] -> nothing to do
+    #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) (coord)
+#else
+    //Opengl => z clip range is [-near, far] -> should remap in theory but dont do it in practice to save some perf (range is close enough)
+    #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) (coord)
+#endif
+
 #endif // UNITY_SHADER_VARIABLES_FUNCTIONS_INCLUDED