Docs: Correct `@access` entry for `WP_User::filter` property.

Add missing `@since` entries for `WP_User::back_compat_keys` and `WP_User::init()`.

Props keesiemeijer, prosti.
Fixes #39502, #39278.

git-svn-id: https://develop.svn.wordpress.org/trunk@39735 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-user.php

@@ -91,13 +91,14 @@ class WP_User {
 	 * The filter context applied to user data fields.
 	 *
 	 * @since 2.9.0
-	 * @access private
+	 * @access public
 	 * @var string
 	 */
-	var $filter = null;
+	public $filter = null;
 
 	/**
 	 * @static
+	 * @since 3.3.0
 	 * @access private
 	 * @var array
 	 */
@@ -159,6 +160,8 @@ class WP_User {
 	/**
 	 * Sets up object properties, including capabilities.
 	 *
+	 * @since  3.3.0
+	 *
 	 * @param object $data    User DB row object.
 	 * @param int    $blog_id Optional. The site ID to initialize for.
 	 */