Improve various @param docs for src/wp-includes/*.

See #30224.


git-svn-id: https://develop.svn.wordpress.org/trunk@30681 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/capabilities.php

@@ -611,6 +611,8 @@ class WP_User {
 	 * Magic method for checking the existence of a certain custom field
 	 *
 	 * @since 3.3.0
+	 * @param string $key
+	 * @return bool
 	 */
 	public function __isset( $key ) {
 		if ( 'id' == $key ) {
@@ -631,6 +633,8 @@ class WP_User {
 	 * Magic method for accessing custom fields
 	 *
 	 * @since 3.3.0
+	 * @param string $key
+	 * @return mixed
 	 */
 	public function __get( $key ) {
 		if ( 'id' == $key ) {