Admin bar: Show the admin bar across all sites when logged in

This shows the admin bar on all sites on WordPress.org once a user is logged in, regardless of permissions on the current site.

See #647

mu-plugins/blocks/global-header-footer/admin-bar.php

@@ -19,7 +19,7 @@
  * @return bool
  */
 function should_show_admin_bar( $show_admin_bar ) {
-	return is_super_admin() || current_user_can( 'read' );
+	return is_super_admin() || is_user_logged_in();
 }
 
 /**