MESA, Ariz. — His bench coach, Randy Knorr, physically held him back. His manager, Davey Johnson, got in his face to try to settle him down. And even after he seemed done pointing, jumping and shouting on the field, he started shouting again from the dugout. ‘‘Edwin Jackson’s very hot,’’ said the voice on the Washington Nationals broadcast even as that Sept.??6 melee between the Cubs and Nationals had settled down. Five months later, during his first day on the other side, the Cubs’ newest big-ticket free agent gets kind of fuzzy on the details. ‘‘I was a peacemaker,’’ Jackson …