Updated AlphaDiscard function to support offsets. Now using it from Particle* shaders.

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Core.hlsl

     #define UNITY_Z_0_FAR_FROM_CLIPSPACE(coord) (coord)
 #endif
 
-void AlphaDiscard(half alpha, half cutoff)
+void AlphaDiscard(half alpha, half cutoff, half offset = 0.0h)
-    clip(alpha - cutoff);
+    clip(alpha - cutoff + offset);
 #endif
 }
 

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Particles.hlsl

 #else
     half result = 1.0h;
 #endif
+    AlphaDiscard(result, _Cutoff, 0.0001h);
-#if defined(_ALPHATEST_ON)
-    clip(result - _Cutoff + 0.0001h);
-#endif
     return result;
 }