Allow reordering other menus

menu_ui_get_menus is deprecated; this patch uses \Drupal\system\Entity\Menu::loadMultiple() instead, fixing /admin/config/pagemenureorder

This checks for the 'node' array key before trying to invoke it. Non-node menu links are not currently included in ReorderMenuForm,

Incorporating the fix from Need bigger range of weights on tabledrag rows 📌 Need bigger range of weights on tabledrag rows RTBC since that no longer applies after the change in #9.