Find an opinionated code formatting tool, like prettier in the JS world

Prettier has an official plugin to format PHP code which might be a good option: https://github.com/prettier/plugin-php

It has some considerations:

* We need to check if it does not conflict with Wordpress coding standard, and if it does, we may want to move to [PER-2](https://www.php-fig.org/per/coding-style/)/[PSR-12](https://www.php-fig.org/psr/psr-12/) instead
* Prettier is a JS tool. Since the project already has a package.json, we could incorporate a JS package manager to the toolbelt and workflow without a lot of effort, but may be easier to introduce a PHP-based tool if such thing exists.