Customize: Improve alignment of WP_Customize_Nav_Menu_Item_Setting::sanitize() behavior with wp_update_nav_menu_item().

* Apply `title_save_pre`, `excerpt_save_pre`, and `content_save_pre` filters on a nav menu item's `title`, `attr_title`, and `description` properties respectively. This ensures that arbitrary markup can be supplied if the user has `unfiltered_html` cap, and for these fields to have markup stripped if not.
* Ensure a nav menu item's `post_status` is sanitized as `publish` or `draft` using the same conditions as `wp_update_nav_menu_item()`.
* Align `WP_Customize_Nav_Menu_Item_Setting::sanitize()` behavior for sanitizing `position` to be the same as `wp_update_nav_menu_item()`.
* Also apply `nav_menu_attr_title` and `nav_menu_description` filters in `WP_Customize_Nav_Menu_Item_Setting::value_as_wp_post_nav_menu_item()` to ensure that previewing markup entered into menu item description will preview the same way as when the nav menu item is saved.
* Add unit tests.

Fixes #32812.

Built from https://develop.svn.wordpress.org/trunk@35580


git-svn-id: http://core.svn.wordpress.org/trunk@35544 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-beta3-35579';
+$wp_version = '4.4-beta3-35580';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.