Create common function for indexing into layered offset buffer

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

     return (eyeOffset + (tileIndex.y * numTilesX) + tileIndex.x);
 }
 
+uint GenerateLayeredOffsetBufferIndex(uint lightCategory, uint2 tileIndex, uint clusterIndex, uint numTilesX, uint numTilesY, int numClusters, uint eyeIndex)
+{
+    // Each eye is split into category, cluster, x, y
+
+    uint eyeOffset = eyeIndex * LIGHTCATEGORY_COUNT * numClusters * numTilesX * numTilesY;
+    int lightOffset = ((lightCategory * numClusters + clusterIndex) * numTilesY + tileIndex.y) * numTilesX + tileIndex.x;
+
+    return (eyeOffset + lightOffset);
+}
+
 #endif

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

 void GetCountAndStartCluster(uint2 tileIndex, uint clusterIndex, uint lightCategory, out uint start, out uint lightCount)
 {
     int nrClusters = (1 << g_iLog2NumClusters);
-    int idx = ((lightCategory * nrClusters + clusterIndex) * _NumTileClusteredY + tileIndex.y) * _NumTileClusteredX + tileIndex.x;
-    
+
-    idx += unity_StereoEyeIndex * LIGHTCATEGORY_COUNT * nrClusters * _NumTileClusteredX * _NumTileClusteredY;
-    
+    const int idx = GenerateLayeredOffsetBufferIndex(lightCategory, tileIndex, clusterIndex, _NumTileClusteredX, _NumTileClusteredY, nrClusters, unity_StereoEyeIndex);
+
     uint dataPair = g_vLayeredOffsetsBuffer[idx];
     start = dataPair & 0x7ffffff;
     lightCount = (dataPair >> 27) & 31;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/lightlistbuild-clustered.compute

     // XRTODO - DONE: Stereo-ize this initial 'offs' to jump into the correct half of g_LayeredOffs.
     // The offsets are organized Category/Cluster/Row/Column.
     // For stereo, we just add eyeIndex*LIGHTCATEGORY_COUNT*nrClusters*nrTilesX*nrTilesY
-    // TODO: Functionalize g_LayeredOffset indexing?
-    uint layeredOffsetBase = eyeIndex * LIGHTCATEGORY_COUNT * (nrClusters*nrTilesX*nrTilesY);
-
-    offs = layeredOffsetBase + (i*nrTilesX*nrTilesY) + (tileIDX.y*nrTilesX) + tileIDX.x;
+    offs = GenerateLayeredOffsetBufferIndex(0, tileIDX, i, nrTilesX, nrTilesY, nrClusters, eyeIndex);
 	for(int category=0; category<LIGHTCATEGORY_COUNT; category++)
 	{
 		int numLights = min(categoryListCount[category],31);		// only allow 5 bits