Missing operator=() implementation in Trapezoid

TrapezoidStruct declares but not defines operator=(), This leads to compilation error when building wrapper in Geant4:

Undefined symbols for architecture x86_64:

  "vecgeom::cxx::TrapezoidStruct<double>::operator=(vecgeom::cxx::TrapezoidStruct<double> const&)", referenced from:

      G4Trap::operator=(G4Trap const&) in G4UTrap.cc.o