stream: Duplex forward writableObjectMode

Duplex did not properly forward writableObjectMode.

Fixes: nodejs#33388

lib/_stream_duplex.js

@@ -75,6 +75,8 @@ ObjectDefineProperties(Duplex.prototype, {
     ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writable'),
   writableHighWaterMark:
     ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableHighWaterMark'),
+  writableObjectMode:
+    ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableObjectMode'),
   writableBuffer:
     ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableBuffer'),
   writableLength:

test/parallel/test-stream-duplex-props.js

@@ -0,0 +1,29 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { Duplex } = require('stream');
+
+{
+  const d = new Duplex({ 
+    objectMode: true,
+    highWaterMark: 100
+  });
+
+  assert.strictEqual(d.writableObjectMode, true);
+  assert.strictEqual(d.writableHighWaterMark, 100);
+}
+
+{
+  const d = new Duplex({
+    readableObjectMode: false,
+    readableHighWaterMark: 10,
+    writableObjectMode: true,
+    writableHighWaterMark: 100
+  });
+
+  assert.strictEqual(d.writableObjectMode, true);
+  assert.strictEqual(d.writableHighWaterMark, 100);
+  assert.strictEqual(d.readableObjectMode, false);
+  assert.strictEqual(d.readableHighWaterMark, 10);
+}