util: implement WHATWG Encoding Standard API

Provide an (initially experimental) implementation of the WHATWG Encoding
Standard API (`TextDecoder` and `TextEncoder`). The is the same API
implemented on the browser side.

By default, with small-icu, only the UTF-8, UTF-16le and UTF-16be decoders
are supported. With full-icu enabled, every encoding other than iso-8859-16
is supported.

This provides a basic test, but does not include the full web platform
tests. Note: many of the web platform tests for this would fail by default
because we ship with small-icu by default.

A process warning will be emitted on first use to indicate that the
API is still experimental. No runtime flag is required to use the
feature.

Refs: https://encoding.spec.whatwg.org/
PR-URL: https://github.com/nodejs/node/pull/13644
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/errors.js

@@ -109,6 +109,10 @@ E('ERR_CPU_USAGE', 'Unable to obtain cpu usage %s');
 E('ERR_DNS_SET_SERVERS_FAILED', (err, servers) =>
   `c-ares failed to set servers: "${err}" [${servers}]`);
 E('ERR_FALSY_VALUE_REJECTION', 'Promise was rejected with falsy value');
+E('ERR_ENCODING_NOT_SUPPORTED',
+  (enc) => `The "${enc}" encoding is not supported`);
+E('ERR_ENCODING_INVALID_ENCODED_DATA',
+  (enc) => `The encoded data was not valid for encoding ${enc}`);
 E('ERR_HTTP_HEADERS_SENT',
   'Cannot render headers after they are sent to the client');
 E('ERR_HTTP_INVALID_STATUS_CODE', 'Invalid status code: %s');