[2.1] Deprecate hooks without standard prefixes

[live627]

Summary

This pull request adds new integration hooks to the Who's Online action processing flow while preserving backward compatibility with existing hooks.

Changes

• Added a new integrate_who_allowed hook before action determination begins, allowing integrations to modify the list of allowed actions used by determineActions().
• Added a new integrate_whos_online_after hook after Who's Online data has been processed, allowing integrations to inspect or modify the generated URL list and user activity data.
• Retained the existing who_allowed and whos_online_after hooks for backward compatibility.
• Added comments marking the legacy hooks as deprecated because they do not follow the standard integrate_ hook naming convention.

Why

The existing hooks were created without the standard integrate_ prefix used throughout SMF's integration system. Adding correctly named hooks provides a consistent API for new integrations while ensuring older modifications continue to function unchanged.

Compatibility

• No breaking changes.
• Existing integrations using who_allowed or whos_online_after will continue to work, but should be updated to use integrate_who_allowed and integrate_whos_online_after instead.

[live627]

Pass $url_data instead of $urls to integrate_whos_online_after so that integrations won't need to do such shenanigans as

// Fix the anomaly where $urls is a string when
// coming from the profile section.
foreach (!is_array($urls) ? [[$urls, 0]] : $urls as $k => $url) {