Add ParticleIDWrapper::negate()

A cheaper way to swap signs on particle ids.

Src/Particle/AMReX_Particle.H

@@ -102,6 +102,17 @@ struct ParticleIDWrapper
         r = (sign) ? lval : -lval;
         return r;
     }
+
+    /** Swap the sign of the id.
+     *
+     * Positive ids become negative and negative ids become positive.
+     */
+    AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
+    void negate () noexcept
+    {
+        // he leftmost bit is our id sign - we will XOR it with 1
+        m_idata ^= static_cast<uint64_t>(1) << 63;
+    }
 };
 
 struct ParticleCPUWrapper