Fix silently dropped WordPress core functions in since-data generator

[ernilambar]

Fixes #1398

Summary

tools/generate-wp-function-since-data.php was silently dropping valid WordPress core functions

Fixes

• @since MU (3.0.0) docblocks not matched — the regex required digits right after @since, so functions using the frozen MU (x.y.z) form (get_active_blog_for_user, wpmu_activate_signup, domain_exists, …) were skipped.
• Root-level core files not scanned — only wp-includes/ and wp-admin/ were scanned, missing global functions in wp-signup.php (confirm_blog_signup), wp-cron.php, and xmlrpc.php.
• Other points mentioned in the related Issue is invalid.

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Co-authored-by: ernilambar <nilambar@git.wordpress.org>
Co-authored-by: davidperezgar <davidperez@git.wordpress.org>
Co-authored-by: frantorres <frantorres@git.wordpress.org>
Co-authored-by: mukeshpanchal27 <mukesh27@git.wordpress.org>

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[Copilot]

Pull request overview

This PR updates the WordPress @since dataset generator to avoid silently skipping valid core functions by expanding the scan scope to include core root PHP files and by enhancing @since parsing to recognize the @since MU (x.y.z) docblock form.

Changes:

• Add a root-level PHP file scan target alongside the existing wp-includes/ and wp-admin/ recursive scans.
• Update the @since extraction regex to support the @since MU (3.0.0) format used by some WordPress MU–ported functions.

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[davidperezgar]

Thanks to Codex’s review, I noticed that glob( $wordpress_dir . '/wp-*.php' ) is broader than the intended core-only scope. It will also scan site-specific root files whose names begin with wp- (for example, wp-maintenance.php), potentially adding their @since-annotated functions to the generated core dataset.

Could we use an explicit allowlist of WordPress core entrypoints instead?