[PHP API Reference] Reduce size of PHP API reference

[mnocon]

Currently, the PHP API reference takes more than 8gb on the disk. With MkDocs build, it's another 8 gb in the site directory -> more than 16gb for a single copy of the doc.

Very often I work on multiple PRs in parallel and I'm running out of disk space to continue some topics.

This also results in slower checkout and clone times when working with the doc.

The size of the repository is caused by our PHP API reference - 3k files, each almost 3mb in size, results in ~8gb of content (that gets doubled after MkDocs built).

This solution extract the common part of each file (the navigation) to a separate file that is loaded using JavaScript.

Advantages:

• repository size is reduced, improving the experience of working with the doc
• PHP API reference PRs start being reviewable and no longer exceed GitHub file limits, making it actually possible to see what has been changed

Disclaimer: I have used AI when writing the code, but I've verified the output (both of the script and the end result) and it works.

When reviewing, review 38bc22b first - and then verify the second commit locally (it's autogenerated).

Link to PHP API ref: https://ez-systems-developer-documentation--3008.com.readthedocs.build/en/3008/api/php_api/php_api_reference/

Individual file before:
https://github.com/ibexa/documentation-developer/blob/5.0/docs/api/php_api/php_api_reference/classes/Ibexa-Contracts-ActivityLog-Values-ActivityLog-Criterion-LogicalAnd.html

Individual file after:
https://github.com/ibexa/documentation-developer/blob/optimize-php-api-ref/docs/api/php_api/php_api_reference/classes/Ibexa-Contracts-ActivityLog-Values-ActivityLog-Criterion-LogicalAnd.html

(becomes actually viewable on GitHub)

============================================================

Navigation extraction complete!

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Files processed: 3202

Navigation file: docs/api/php_api/php_api_reference/shared-navigation.html

Navigation size: 2,484,805 bytes (2.37 MB)

Original total size: 8,006,126,043 bytes (7.46 GB)

Modified total size: 95,471,198 bytes (0.09 GB)

Tested scenarios:

1. Navigation works for namespaces - ✅
2. Navigation works for classes - ✅
3. Navigation works for the index file - ✅
4. Navigation works for the error report file - ✅
5. Scroll position is saved when navigating - ✅
6. The currently selected file is correctly highlighted - ✅
7. The message with disabled JS is correct - ✅
8. The loading message is displayed correctly - ✅
9. The error message is correct in case of network error - ✅

[github-actions]

Preview of modified files

Preview of addition to PHP API Reference:

• ``