* Request full refresh if there are nav menu instances that lack partials for a changed setting.
* Restore `WP_Customize_Nav_Menus::$preview_nav_menu_instance_args` and `WP_Customize_Nav_Menus::export_preview_data()` from 4.3, and keeping a tally of all `wp_nav_menu()` calls regardless of whether they can use selective refresh.
* Ensure that all instances of `wp_nav_menu()` are tallied, regardless of whether they are made during the initial preview call or during subsequent partial renderings. Export `nav_menu_instance_args` with each partial rendering response just as they are returned when rendering the preview as a whole.
* Fix issues with Custom Menu widget where nav menu items would fail to render when switching between menus when a menu lacked items to begin with.
* Make sure the fallback behavior is invoked when the partial is no longer associated with a menu.
* Do fallback behavior to refresh preview when all menu items are removed from a menu.
Follows [36586].
See #27355.
Fixes#35362.
git-svn-id: https://develop.svn.wordpress.org/trunk@36889 602fd350-edb4-49c9-b593-d223f7449a82
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