Add @static* annotations where they are missing.

Initialize all static vars that are not, most to `null`.

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32650 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/capabilities.php

@@ -489,6 +489,11 @@ class WP_User {
 	 */
 	var $filter = null;
 
+	/**
+	 * @static
+	 * @access private
+	 * @var array
+	 */
 	private static $back_compat_keys;
 
 	/**
@@ -562,6 +567,8 @@ class WP_User {
 	 *
 	 * @since 3.3.0
 	 *
+	 * @static
+	 *
 	 * @global wpdb $wpdb
 	 *
 	 * @param string $field The field to query against: 'id', 'slug', 'email' or 'login'