Use BitFieldInsert() in CopySign()

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/Common.hlsl

     {
         uint negZero = 0x80000000u;
         uint signBit = negZero & asuint(s);
-        return asfloat(signBit | asuint(abs(x)));
+        return asfloat(BitFieldInsert(negZero, signBit, x));
     }
 #else
     return (s >= 0) ? abs(x) : -abs(x);