airframe-http (js): Use Fetch API instead of Ajax

[xerial]

dom.ext.Ajax has been deprecated. It's better to use native dom.Fetch API:

Usage:
scala-js/scala-js-dom#627 (comment)

https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch

[xerial]

WIP #3370 but two compliations

• Fetch API access works only in Web browsers, so we still need Ajax
• Node.js has node-fetch, but its API can't be accessed through scalajs-dom at this moment.

Related
https://stackoverflow.com/questions/70380171/ajax-post-dom-fetch/70412242#70412242

[xerial]

As Fetch API in scala-js-dom will not fully replace the XMLHttpRequest in Node.js, Ajax code will remain for a while.