Multisite: Add WP_Site_State class for efficient site state management

[Sukhendu2002]

Trac ticket: https://core.trac.wordpress.org/ticket/37958

This PR adds a new WP_Site_State class and corresponding helper functions that provide methods for managing site state in WordPress Multisite.

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Props sukhendu2002, tfrommen.

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[tfrommen]

Thank you for upgrading my 8-year-old patch to 2025, and turning it into a GitHub PR. 🙏

I left some inline comments, none blocking at all.

Has the wp_xmlrpc_server class not been updated deliberately? I know it's not something many people use (and is even recommended against in many contexts), but still.

[tfrommen]

It doesn't make much of a difference, but this could also be done in wp-includes/ms-settings.php, making this function pure.

[Sukhendu2002]

That's a great suggestion. Moving the require to ms-settings.php would make the get_site_state() function more efficient. I'll implement this change.

[tfrommen]

I wonder if we really need this function. Looking at the Locale API, there is no function to restore locales. It's always done using the relevant method on the (global) locale switcher class instance.

Personally, I think having the above factory function is fine, but doing $site_state->restore(); instead of restore_site_state( $site_state ); feels more natural, and also in line with several other classes that don't have API function wrappers around them.

Thoughts?

[Sukhendu2002]

I see your point about directly using the class method instead of a wrapper. I initially created the wrapper function because it follows the pattern used for switch_to_blog() and restore_current_blog()

However, I'm open to removing it if you feel the direct method call is more appropriate. The Locale API example you mentioned makes sense.

[Sukhendu2002]

Hey @tfrommen, Thank you for reviewing the PR! I really appreciate your detailed feedback.

You're right, I didn't update the XML-RPC class since I was focusing on the core multisite functionality first. I can certainly look at improving this class too if you think it would be valuable.

I'll update the PR with fixes for the identified issues!