Use promisified fs.readFile instead of fs.promises.readFile (#18204)

* Create a readFileAsync wrapper module

* Use the readFileAsync wrapper module instead of fs.promises.readFile

* Fix require path in test

lib/readfile-async.js

@@ -0,0 +1,6 @@
+const fs = require('fs')
+const util = require('util')
+
+// This is faster than using `fs.promises.readFile` for the time being
+// See: https://github.com/nodejs/node/issues/37583
+module.exports = util.promisify(fs.readFile)