core: Use lazy message formatting in checkState (#12144)

Author: shivaspeaks

core/src/main/java/io/grpc/internal/InternalSubchannel.java

@@ -346,7 +346,7 @@ private void gotoState(final ConnectivityStateInfo newState) {
 
     if (state.getState() != newState.getState()) {
       Preconditions.checkState(state.getState() != SHUTDOWN,
-          "Cannot transition out of SHUTDOWN to " + newState);
+          "Cannot transition out of SHUTDOWN to %s", newState.getState());
       if (reconnectDisabled && newState.getState() == TRANSIENT_FAILURE) {
         state = ConnectivityStateInfo.forNonError(IDLE);
       } else {