process: use public readableFlowing property

PR-URL: #29502
Refs: #445
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

lib/internal/process/stdio.js

@@ -123,7 +123,7 @@ function getMainThreadStdio() {
     function onpause() {
       if (!stdin._handle)
         return;
-      if (stdin._handle.reading && !stdin._readableState.flowing) {
+      if (stdin._handle.reading && !stdin.readableFlowing) {
         stdin._readableState.reading = false;
         stdin._handle.reading = false;
         stdin._handle.readStop();