AJAX page state is now a request attribute

The ajax_page_state query parameter or request key holds information about previously loaded libraries, so that AJAX requests only add new libraries that are needed.

This is usually transparent and handled automatically, but following changes upstream in Symfony the ajax_page_state is added as a request attribute in early middleware. Any code that previously looked in the query string or request directly for the state should now look in the request attributes instead.

Previously:

$ajax_page_state = $request->get('ajax_page_state');
// or
$ajax_page_state = $request->query->get('ajax_page_state');

Becomes:

$ajax_page_state = $request->attributes->get('ajax_page_state');