Posts: Introduce WP_Post_Type and use it in register_post_type() and unregister_post_type().

This changes the global `$wp_post_types` to an array of `WP_Post_Type` objects. `WP_Post_Type` includes methods to handle post type supports, rewrite rules, meta boxes, hooks, and taxonomies.
Each post type argument becomes a property of `WP_Post_Type`.

Props swissspidy, flixos90.
Fixes #36217.

git-svn-id: https://develop.svn.wordpress.org/trunk@37890 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-posts-list-table.php

@@ -72,8 +72,8 @@ class WP_Posts_List_Table extends WP_List_Table {
 	 *
 	 * @see WP_List_Table::__construct() for more information on default arguments.
 	 *
-	 * @global object $post_type_object
-	 * @global wpdb   $wpdb
+	 * @global WP_Post_Type $post_type_object
+	 * @global wpdb         $wpdb
 	 *
 	 * @param array $args An associative array of arguments.
 	 */