Uses html-eslint for HTML file and eslint-plugin-html for inline
JavaScript.
Use HTML5 (not XHTML), remove CDATA and trailing slashes for self
closing tags.
Add format checks to CI.
This makes it easier to set up, as you always have Python installed
when building Godot. On the other hand, you don't always have Node.js
+ npm installed (and you may not want to spend time running `npm install`).
Co-authored-by: Fabio Alessandrelli <fabio.alessandrelli@gmail.com>
