Added a library function to get NDC with the Z component

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/Common.hlsl

 // (position = positionCS) => (clipSpaceTransform = use default)
 // (position = positionVS) => (clipSpaceTransform = UNITY_MATRIX_P)
 // (position = positionWS) => (clipSpaceTransform = UNITY_MATRIX_VP)
-float2 ComputeNormalizedDeviceCoordinates(float3 position, float4x4 clipSpaceTransform = k_identity4x4)
+float3 ComputeNormalizedDeviceCoordinatesWithZ(float3 position, float4x4 clipSpaceTransform = k_identity4x4)
 {
     float4 positionCS = ComputeClipSpacePosition(position, clipSpaceTransform);
 
     positionCS.y = -positionCS.y;
 #endif
 
-    return positionCS.xy * (rcp(positionCS.w) * 0.5) + 0.5;
+    positionCS *= rcp(positionCS.w);
+    positionCS.xy = positionCS.xy * 0.5 + 0.5;
+
+    return positionCS.xyz;
+}
+
+// Use case examples:
+// (position = positionCS) => (clipSpaceTransform = use default)
+// (position = positionVS) => (clipSpaceTransform = UNITY_MATRIX_P)
+// (position = positionWS) => (clipSpaceTransform = UNITY_MATRIX_VP)
+float2 ComputeNormalizedDeviceCoordinates(float3 position, float4x4 clipSpaceTransform = k_identity4x4)
+{
+    return ComputeNormalizedDeviceCoordinatesWithZ(position, clipSpaceTransform);
 }
 
 float3 ComputeViewSpacePosition(float2 positionNDC, float deviceDepth, float4x4 invProjMatrix)

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/LightLoopDef.hlsl

         if (cacheType == ENVCACHETYPE_TEXTURE2D)
         {
             //_Env2DCaptureVP is in capture space
-            float4 ndc = ComputeClipSpacePosition(texCoord, _Env2DCaptureVP[index]);
-            ndc *= rcp(ndc.w);
-            ndc.xy = ndc.xy * 0.5 + 0.5;
+            float3 ndc = ComputeNormalizedDeviceCoordinatesWithZ(texCoord, _Env2DCaptureVP[index]);
 
             color.rgb = SAMPLE_TEXTURE2D_ARRAY_LOD(_Env2DTextures, s_trilinear_clamp_sampler, ndc.xy, index, 0).rgb;
             color.a = any(ndc.xyz < 0) || any(ndc.xyz > 1) ? 0.0 : 1.0;