test: improve code coverage for i18n

Coverage report for src/node_i18n.cc shows that the
Has() method is not covered. This test adds coverage
for that method.

PR-URL: #25428
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-icu-punycode.js

@@ -7,6 +7,12 @@ if (!common.hasIntl)
 const icu = process.binding('icu');
 const assert = require('assert');
 
+// test hasConverter method
+assert(icu.hasConverter('utf-8'),
+       'hasConverter should report coverter exists for utf-8');
+assert(!icu.hasConverter('x'),
+       'hasConverter should report coverter does not exist for x');
+
 const tests = require('../fixtures/url-idna.js');
 const wptToASCIITests = require('../fixtures/url-toascii.js');