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.
Built from https://develop.svn.wordpress.org/trunk@37890


git-svn-id: http://core.svn.wordpress.org/trunk@37831 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/edit-form-advanced.php

@@ -11,9 +11,9 @@ if ( !defined('ABSPATH') )
 	die('-1');
 
 /**
- * @global string  $post_type
- * @global object  $post_type_object
- * @global WP_Post $post
+ * @global string       $post_type
+ * @global WP_Post_Type $post_type_object
+ * @global WP_Post      $post
  */
 global $post_type, $post_type_object, $post;