lib: use null-prototype objects for property descriptors

Refs: https://github.com/nodejs/node/pull/42921

PR-URL: https://github.com/nodejs/node/pull/43270
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

lib/string_decoder.js

@@ -140,6 +140,7 @@ StringDecoder.prototype.text = function text(buf, offset) {
 
 ObjectDefineProperties(StringDecoder.prototype, {
   lastChar: {
+    __proto__: null,
     configurable: true,
     enumerable: true,
     get() {
@@ -149,6 +150,7 @@ ObjectDefineProperties(StringDecoder.prototype, {
     }
   },
   lastNeed: {
+    __proto__: null,
     configurable: true,
     enumerable: true,
     get() {
@@ -156,6 +158,7 @@ ObjectDefineProperties(StringDecoder.prototype, {
     }
   },
   lastTotal: {
+    __proto__: null,
     configurable: true,
     enumerable: true,
     get() {