* Allow `WP_Customize_Nav_Menus::insert_auto_draft_post()` to take full post array to pass to `wp_insert_post()`, except for `post_status`. Require `post_title`.
* Ensure empty `post_name` gets explicitly set to slugified `post_title`.
* Explicitly allow only `post_type` and `post_title` params in `WP_Customize_Nav_Menus::ajax_insert_auto_draft_post()`.
* Use `wp_update_post()` instead of `wp_publish_post()` to ensure unique slugs are assigned to published auto-draft posts.
* Re-use `WP_Customize_Nav_Menus::insert_auto_draft_post()` when inserting stubs from starter content.
See #38114, #38013, #34923.
Fixes#38539.
git-svn-id: https://develop.svn.wordpress.org/trunk@39038 602fd350-edb4-49c9-b593-d223f7449a82