Temporarily disable tone mapping of volumetrics to avoid banding artifacts

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VBuffer.hlsl

                                 bool   quadraticFilterXY)
 {
     // TODO: add some slowly animated noise to the reconstructed value.
-    return FastTonemapInvert(SampleVBuffer(TEXTURE3D_PARAM(VBufferLighting, clampSampler),
+    // TODO: re-enable tone mapping after implementing pre-exposure.
+    return /*FastTonemapInvert*/(SampleVBuffer(TEXTURE3D_PARAM(VBufferLighting, clampSampler),
                                            positionNDC,
                                            linearDepth,
                                            VBufferResolution,

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VolumetricLighting.compute

         // Note: for correct filtering, the data has to be stored in the perceptual space.
         // This means storing the tone mapped radiance and transmittance instead of optical depth.
         // See "A Fresh Look at Generalized Sampling", p. 51.
-        _VBufferLightingIntegral[voxelCoord] = float4(FastTonemap(totalRadiance), Transmittance(opticalDepth));
+        // TODO: re-enable tone mapping after implementing pre-exposure.
+        _VBufferLightingIntegral[voxelCoord] = float4(/*FastTonemap*/(totalRadiance), Transmittance(opticalDepth));
 
         // Compute the optical depth up to the end of the interval.
         opticalDepth += 0.5 * extinction * dt;