test: add Unicode characters regression test

This test ensures that UTF-8 characters can be used in core JavaScript
modules built into Node's binary.

PR-URL: https://github.com/nodejs/node/pull/11423
Ref: https://github.com/nodejs/node/pull/11129
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/test/unicode.js

@@ -0,0 +1,6 @@
+'use strict';
+
+// This module exists entirely for regression testing purposes.
+// See `test/parallel/test-internal-unicode.js`.
+
+module.exports = '✓';