emit from MatrixEvent.makeReplaced instead of Room

now that event can be replaced from Relations instead of Room

Also make `makeReplaced` non-destructive by not touching the original
event.content, so it can be undone by later calls.

src/client.js

@@ -4168,6 +4168,10 @@ function _PojoToMatrixEventMapper(client) {
             ]);
             event.attemptDecryption(client._crypto);
         }
+        const room = client.getRoom(event.getRoomId());
+        if (room) {
+            room.reEmitter.reEmit(event, ["Event.replaced"]);
+        }
         return event;
     }
     return mapper;