Hooks generator does not get all the PHP files to scan

Context

At Ventures team we would like to generate a hooks document for our internal use and we found there is an awesome script in this repo that just do the things we want. Here's our PR woocommerce/google-listings-and-ads#1573, it basically copy most of the code from the script and then modify a bit to suit what we need.

The Problem

We found the script does not capture all the PHP files in the directory, the TLDR reason is the script cannot work in the case where there are more than two levels of paths. Please see the detailed explanation in our PR's comment: https://github.com/woocommerce/google-listings-and-ads/pull/1573#issuecomment-1173318631.

It also relates to #15.

Our solution may not fulfil the needs in this repo, also if there's any better ways to generate hooks documents (like using PHPDoc?) in your mind, we're happy to hear and learn about.

Start with the referenced generate-hook-docs.php script and review the detailed explanation in the linked google-listings-and-ads PR comment. Reproduce the generator against a directory with more than two levels of paths, then verify that all PHP files and their hooks are included in the generated document.