Fix links array structure

[darrenoh]

No description provided.

[mglaman]

Actually, I also forgot about this:

            if (method_exists(HookPreprocess::class, $theme_hook)) {
                $cache[$theme_hook]['preprocess functions'][] = HookPreprocess::class . '::' . $theme_hook;
            }

So we can move the function into that class.

[darrenoh]

I'm having second thoughts about using a preprocess function on HookPreprocess. I don't want to modify every links array, just those that Drupal 7 modules pass to the theme() function. I think HookPreprocess should be used to modify variables going from Drupal 10 to Drupal 7 themes.