lib: move encodingsMap to internal/util

PR-URL: https://github.com/nodejs/node/pull/51044
Refs: https://github.com/nodejs/performance/issues/136
Reviewed-By: Vinícius Lourenço Claro Cardoso <contact@viniciusl.com.br>
Reviewed-By: Yagiz Nizipli <yagiz.nizipli@sentry.io>

lib/string_decoder.js

@@ -38,15 +38,18 @@ const {
   kSize,
   decode,
   flush,
-  encodings,
 } = internalBinding('string_decoder');
-const internalUtil = require('internal/util');
+const {
+  kIsEncodingSymbol,
+  encodingsMap,
+  normalizeEncoding: _normalizeEncoding,
+} = require('internal/util');
 const {
   ERR_INVALID_ARG_TYPE,
   ERR_INVALID_THIS,
   ERR_UNKNOWN_ENCODING,
 } = require('internal/errors').codes;
-const isEncoding = Buffer[internalUtil.kIsEncodingSymbol];
+const isEncoding = Buffer[kIsEncodingSymbol];
 
 const kNativeDecoder = Symbol('kNativeDecoder');
 
@@ -60,7 +63,7 @@ const kNativeDecoder = Symbol('kNativeDecoder');
  * @throws {TypeError} Throws an error when encoding is invalid
  */
 function normalizeEncoding(enc) {
-  const nenc = internalUtil.normalizeEncoding(enc);
+  const nenc = _normalizeEncoding(enc);
   if (nenc === undefined) {
     if (Buffer.isEncoding === isEncoding || !Buffer.isEncoding(enc))
       throw new ERR_UNKNOWN_ENCODING(enc);
@@ -69,10 +72,6 @@ function normalizeEncoding(enc) {
   return nenc;
 }
 
-const encodingsMap = {};
-for (let i = 0; i < encodings.length; ++i)
-  encodingsMap[encodings[i]] = i;
-
 /**
  * StringDecoder provides an interface for efficiently splitting a series of
  * buffers into a series of JS strings without breaking apart multi-byte