HDRenderPipeline: fix issue with _AlphaCutoffPostpass

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/LitDataIndividualLayer.hlsl

 
     // Perform alha test very early to save performance (a killed pixel will not sample textures)
 #if defined(_ALPHATEST_ON) && !defined(LAYERED_LIT_SHADER)
-    DoAlphaTest(alpha, _AlphaCutoff);
+    float alphaCutoff = _AlphaCutoff;
+    #ifdef CUTOFF_TRANSPARENT_DEPTH_POSTPASS
+    alphaCutoff = _AlphaCutoffPostpass;
+    #endif
+    DoAlphaTest(alpha, alphaCutoff);
 #endif
 
     float3 detailNormalTS = float3(0.0, 0.0, 0.0);

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/LitProperties.hlsl

 
 // shared constant between lit and layered lit
 float _AlphaCutoff;
+float _AlphaCutoffPostpass;
 float4 _DoubleSidedConstants;
 float _DistortionScale;
 float _DistortionVectorScale;