hook_menu() defaults to putting menu items in an internal 'hidden' menu

In order to avoid the unnecessary processing of dozens of hidden links on each page load, Backdrop now defaults to putting menu items defined in hook_menu() into a hidden 'internal' menu. Previously they were added to the 'main-menu' by default.

As a result, menu items that should be shown in the main menu now need to explicitly define this. For example:

$item['menu_name'] = 'main-menu';