Observation of Pr and Gd ordering in the 2212-type compounds (\({\mathrm{Pb}}_{0.5}\( {\mathrm{Cu}}_{0.5}\) {)}_{2}\)(\({\mathrm{Ba}}_{0.5}\( {\mathrm{Sr}}_{0.5}\) {)}_{2}\)R$ {\mathrm{Cu}}_{2}$\({\mathrm{O}}_{8}\)(R=Pr,Gd)