parse-sax: use native TextDecoder in browser when available

Doing a profiling in chrome browser shows that the `Buffer.toString()` is using unexpected long cpu time. With the native TextDecoder it can get much faster in browsers supporting it.
In browsers not supporting TextDecoder, like Internet Explorer, we can fallback to `Buffer.toString()`.

References:
feross/buffer#268
feross/buffer#60
https://developer.mozilla.org/en-US/docs/Web/API/TextDecoder

lib/utils/parse-sax.js

@@ -1,6 +1,15 @@
 const {SaxesParser} = require('saxes');
 const {PassThrough} = require('readable-stream');
 
+// eslint-disable-next-line node/no-unsupported-features/node-builtins
+const textDecoder = typeof TextDecoder === 'undefined' ? null : new TextDecoder('utf-8');
+function toUtf8String(chunk) {
+  if (textDecoder) {
+    return textDecoder.decode(chunk);
+  }
+  return chunk.toString();
+}
+
 module.exports = async function*(iterable) {
   // TODO: Remove once node v8 is deprecated
   // Detect and upgrade old streams
@@ -17,7 +26,7 @@ module.exports = async function*(iterable) {
   saxesParser.on('text', value => events.push({eventType: 'text', value}));
   saxesParser.on('closetag', value => events.push({eventType: 'closetag', value}));
   for await (const chunk of iterable) {
-    saxesParser.write(chunk.toString());
+    saxesParser.write(toUtf8String(chunk));
     // saxesParser.write and saxesParser.on() are synchronous,
     // so we can only reach the below line once all events have been emitted
     if (error) throw error;