Pass the previous menu_link $item when calling menu_link_insert/menu_link_update

Investigating slow menu_rebuild():

#2511696: i18n_menu_menu_link_update() makes menu_rebuild() 17% slower.

Found that core could pass the previous menu_item when calling the menu_link_insert/menu_link_update hooks so that contrib have additional information about the changes being done to the menu item.