chore(async-rewriter2): add small helper cli for testing (#798)

I’ve used this during development a few times recently,
so it might make sense to just commit it.

Author: addaleax

packages/async-rewriter2/bin/async-rewrite.js

@@ -0,0 +1,8 @@
+#!/usr/bin/env node
+/* eslint-disable strict, no-sync */
+'use strict';
+const AsyncWriter = require('../').default;
+const fs = require('fs');
+const input = fs.readFileSync(process.argv[2]);
+const asyncWriter = new AsyncWriter();
+process.stdout.write(asyncWriter.process(input));