punycode: add pending deprecation

PR-URL: nodejs#38444
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/punycode.js

@@ -1,5 +1,15 @@
 'use strict';
 
+const { getOptionValue } = require('internal/options');
+if (getOptionValue('--pending-deprecation')){
+	process.emitWarning(
+		'The `punycode` module is deprecated. Please use a userland ' +
+		'alternative instead.',
+		'DeprecationWarning',
+		'DEP0040',
+	);
+}
+
 /** Highest positive signed 32-bit float value */
 const maxInt = 2147483647; // aka. 0x7FFFFFFF or 2^31-1